What is a compound word: Compound Words: Open, Closed, or Hyphenated?

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Rules for compound words | Merriam-Webster


How do you decide whether a compound should be written as one word, separate words, or hyphenated words?

Compounds

A compound is a word or word group that consists of two or more parts that work together as a unit to express a
specific concept. Compounds can be formed by combining two or more words (as in double–check,
cost–effective, farmhouse, graphic equalizers, park bench, around–the–clock, or son of a gun), by combining prefixes or suffixes with words (as in ex–president, shoeless, presorted, or uninterruptedly), or by combining two or more word elements (as in macrophage or photochromism). Compounds are written in one of three ways: solid (as in cottonmouth), hyphenated (screenwriter–director), or open (health care). Because of the variety of standard practice, the choice among the styles for a given compound represents one of the most common and vexing of all style issues writers encounter.


Compounds in the Dictionary

A good dictionary will list many permanent compounds, compounds so commonly used that they have become
permanent parts of the language. However, a dictionary generally will not list temporary compounds, those
created to meet a writer’s need at a particular moment. Most compounds whose meanings are self–evident from the
meanings of their component words also will not be listed in the dictionary, even if they are permanent and
widely used.


The Compound–styling Conundrum

When compounds begin to be used widely, there may be significant variation in how writers style them, and it can
take years to achieve a high degree of consistency in their format. For many terms, it is often completely acceptable
to choose freely among open, hyphenated, and closed alternatives, even though the term has been used in English for
an extended period (for instance, lifestyle, life–style, or life style). Although the
styling that ultimately takes hold for a compound may be determined by nothing more than editorial preference, there
is one pattern that often holds true as new compounds become entrenched in English. Compound nouns are usually written
as one word, compound verbs are generally written as two, and compound adjectives are very often written with a
hyphen.


Styling Internet– and Computer–Related Terms (e.g., on–line, website, e–mail)

Internet–related compounds are still so new that their preferred styling remains in flux, with the same compound
styled different ways in different publications. Over time, they will likely become more consistent, but what should
writers do now? The following list provides the Internet–term stylings that are currently most widely used in
professionally edited, published writing.

  • E–mail (with a capital E when used as a noun)
  • e–mail (with a lowercase e when used as a verb)
  • online
  • Web site
  • Web page
  • e–book
  • e–tail
  • webcam
  • webcast/webcaster
  • webmaster (often cap)
  • dot–com

Text for this article was adapted from Merriam-Webster’s Manual for Writers and Editors.

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Compound Words | Types, List & Definition

Published on
April 3, 2023
by

Jack Caulfield.

Revised on
July 3, 2023.

compound word (sometimes just called a compound) is a series of two or more words that collectively form a single word. There are three types of compound words, which differ in terms of how they are written:

  • An open compound word is written with spaces between the words (e.g., “high school”).
  • A hyphenated compound word is written with hyphens between the words (e.g., “sister-in-law”).
  • A closed compound word is written with no spaces or punctuation (e.g., “cheesecake”).

TipIf you’re confused about how to write a particular compound word or about whether it qualifies as a compound at all, check out our articles on commonly confused words (e. g., “everyday” vs. “every day”) and on common mistakes (e.g., “now a days” vs. “nowadays”).

For any words and phrases that we don’t cover, it’s best to consult a reliable dictionary like Merriam-Webster.

Table of contents

  1. Open compound words
  2. Hyphenated compound words
  3. Closed compound words
  4. List of compound words
  5. Pluralizing compound nouns
  6. Compound words vs. other types of words
  7. Worksheet: Compound words
  8. Other interesting articles
  9. Frequently asked questions about compound words

Open compound words

Open compound words are written with spaces between the individual words. For example, “compound word” itself is an open compound word.

Open compounds are normally fairly new terms or are used only in specialist contexts. Over time, as they become more widely used, they tend to become hyphenated or closed compounds. But this is not universal: some well-established compounds such as “high school” continue to be written with spaces.

Many open compound words function as nouns and are formed by combining a noun with another noun or with an adjective.

Examples: Open compound nounsMy favorite part of the theme park was the roller coasters.

Some search engines are experimenting with incorporating artificial intelligence into their services.

Phrasal verbs are also normally written as open compounds. A phrasal verb is a series of two or more words (often a verb and a preposition) that functions collectively as a verb.

Examples: Phrasal verbsShe couldn’t figure out the solution to the riddle.

Should I go ahead and log in, or should I hold off for now?

Note that normally open compounds are instead written as hyphenated or closed compounds in certain contexts. A compound noun is often hyphenated or closed when it’s used attributively (functioning as an adjective before another noun) or as a verb, and a phrasal verb is hyphenated or closed when it’s used as a noun.

Examples: Hyphenating or closing normally open compoundsIt’s a commonsense solution to a complicated problem.

She’s gone to test-drive a new car.

Kenan gave me the go-ahead and forwarded my new login details.

Hyphenated compound words

Hyphenated compound words are written with hyphens connecting the words. For example, “well-being” is a hyphenated compound word.

Hyphenated compounds are typically noun phrases being used as adjectives (e.g. “long-term”) or as verbs (e.g., “strong-arm”) or verb phrases being used as nouns (e.g., “check-in”) or as adjectives (e.g., “mind-blowing”).

Compound nouns were quite commonly hyphenated in the past but mostly aren’t now (e.g., “walking-stick” and “living-room” are now usually written “walking stick” and “living room”). But some remain hyphenated, especially if they consist of three or more words (e.g., “father-in-law”).

Examples: Hyphenated compound wordsMy sisters-in-law are coming to stay on Saturday.

You could see what over-the-counter medication is available, or there’s a walk-in clinic down the street.

A shoplifter had a run-in with an off-duty police officer who caught him red-handed.

TipSince there are many compounds that are normally open but hyphenated when used in certain ways, people often struggle to understand when they should hyphenate a given term. Check out our article on hyphens for more in-depth guidance on specific hyphenation issues.

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Closed compound words

Closed compound words are written without hyphens or spaces. For example, “babysitter” is a closed compound word.

Closed compounds can play a wide variety of roles, functioning as nouns (e. g., “weekend”), pronouns (e.g., “herself”), prepositions (e.g., “into”), adverbs (e.g., “however”), adjectives (e.g., “barefoot”), conjunctions (e.g., “whereas”), or verbs (e.g., “snowball”).

Closed compounds tend to be well-established words. They often start out as open compounds but close over time as they become more familiar. For example, compound indefinite pronouns used to be written as open compounds (e.g., “every one,” “some thing”), but now all except “no one” are closed.

Examples: Closed compound wordsI cannot wait for the weekend. I’m going backpacking with my boyfriend!

Andrea couldn’t function without his breakfast.

Few people want to babysit a newborn child.

List of compound words

The table below provides a representative selection of compound words, categorized by whether they are open, hyphenated, or closed and by what part of speech they function as.

You can observe some patterns in the table. For instance, there are many compound nouns; compound adjectives tend to be hyphenated; and some parts of speech only form compounds in certain ways.

Note that some words appear as more than one part of speech but may be written differently depending on their function. There may also be multiple ways of writing a single compound (e.g., “login” or “log-in”). Consult a dictionary if you’re unsure.

List of compound words
Part of speech Open compounds Hyphenated compounds Closed compounds
Noun artificial intelligence, attorney general, common sense, French fries, high school, house party, living room, roller coaster, search engine, test drive, theme park, walking stick check-in, go-ahead, kick-off, know-it-all, man-of-war, merry-go-round, run-in, runner-up, sister-in-law, well-being backpack, boyfriend, breakfast, bypass, checkout, cheesecake, highway, login, newborn, payout, peanut, smartphone, weekend, wherewithal
Pronoun each other, no one, one another anyone, everything, nobody, oneself, themselves
Verb check in, figure out, go ahead, hold off, kick off, log in, pass by, used to strong-arm, test-drive babysit, breakfast, bypass, cannot, snowball
Adjective empty-handed, full-fledged, lightning-fast, long-term, mind-blowing, off-duty, over-the-counter, roller-coaster, run-of-the-mill, up-to-date, walk-in commonsense, everyday, heartbreaking, nearby, newborn, shamefaced, spellbinding
Adverb after all, en route, next to, with feeling lightning-fast, mind-blowingly, red-handed anymore, anyway, awhile, elsewhere, hereby, however, maybe, moreover, nevertheless, nowadays, spellbindingly
Preposition as far as, close by, such as, next to, with regard to insofar, into, throughout, upon, within
Conjunction as far as, in that whenever, whereas
Determiner another, whatever, whichever

Pluralizing compound nouns

When you want to pluralize a noun that consists of multiple words, it can be difficult to know which word to pluralize. In a closed compound, it’s easy: the pluralization always comes at the end, since it’s written as one word (e.g., “backpacks,” “houseboats,” “payouts”).

In open and hyphenated compounds, it varies; the final word is sometimes pluralized (e.g., “high schools,” “know-it-alls”), but sometimes an earlier word is instead (e.g., “attorneys general,” “men-of-war”). Usually, only one word is pluralized (e.g., “men-of-wars” is wrong).

To understand which word should be pluralized, look at the compound logically and consider which word “heads” the group—in other words, which one represents the thing being named?

  • Frenches fry [Frenches that are fry?]
  • French fries [Fries that are French]
  • sister-in-laws [a sister (in multiple laws)?]
  • sisters-in-law [multiple sisters (in law)]

But, admittedly, it can be hard to apply this logic in some cases (e.g., “merry-go-rounds”). If in doubt about how to pluralize a term, check a dictionary, where the correct plural noun will be listed in the entry.

Compound words vs. other types of words

Compound words are one way of combining multiple words into one unit, but there are other ways too. Read on to see how compound words differ from:

  • Portmanteaus
  • Contractions
  • Acronyms
  • Simple and complex words

Portmanteaus

portmanteau (also called a blend) is a word created by blending two words together. A portmanteau is different from a closed compound word because at least one of the words making it up is not used in its complete form: some letters have been removed or moved around.

For example, the portmanteau “chortle” is a combination of “chuckle” and “snort.” A part of the word “snort” has been inserted in the middle of the word “chuckle,” but neither word appears in full. As a closed compound, it might be “chucklesnort” or “snortchuckle” (not real words).

Examples: PortmanteausSmog [smoke + fog] is a persistent danger in heavily industrialized environments.

The concept of the multiverse [multiple + universe] describes the collection of all the possible universes in existence.

Jazzercise [jazz + exercise] is a form of aerobic exercise based on jazz dancing.

Contractions

Contractions are shortenings of existing words where the omitted letters are usually (not always) marked by an apostrophe. Sometimes, a contraction is a single word with some letters omitted (e.g., “talkin’”), but most commonly, it’s two or more words combined (e.g., “don’t,” “it’s,” “wanna”).

Combining contractions like this differ from compound words, again, because they don’t include the full words they are formed from: some letters are replaced with apostrophes and not pronounced.

Another difference is that contractions, especially less common ones like “wouldn’t’ve,” are generally avoided in formal contexts like academic writing, whereas there’s no problem with using compound words in such contexts.

Examples: ContractionsC’mon, let’s go! We’ve gotta hurry.

It’s hard for me to see why you don’t like the plan if you won’t explain your objections to it.

Acronyms

An acronym is another way of shortening a series of words into one unit, in this case by reducing each word to its first letter (e.g., “NATO”: “North Atlantic Treaty Organization”) or occasionally its first syllable (e.g., “Benelux”: “Belgium, Netherlands, Luxembourg”).

Some acronyms are pronounced as full words (e.g. “NATO” is [nay-toe]), while others, often called initialisms, are pronounced as individual letters (e.g., “BBC” is [bee-bee-see]).

Again, they differ from compound words because they don’t include the full words that are being combined. Acronyms are fine to use in academic writing, as long as you define them on first use.

Examples: ContractionsThe WHO [World Health Organization] named the new disease “COVID-19” (short for “coronavirus disease 2019”).

Simple and complex words

Simple words are words that cannot be broken down into smaller meaningful pieces. For example, “run” is a simple word—you could break it down into “ru” and “n,” but it’s clear that these don’t have any meaning on their own.

Complex words are composed of parts that each contribute some meaning to the whole. For example, “runner” consists of “run” (the verb it’s derived from, describing the action in question) and “-er” (a suffix used to indicate a person who does the action).

These individual units of sense are called morphemes: a simple word consists of just one morpheme, while a complex word consists of a main morpheme (called the root; “run” in our example) plus at least one other morpheme.

A compound word differs from a complex word because it’s made up of complete words that could also stand alone. In “runner,” it’s clear that while “run” is a word in its own right, “-er” is not. In contrast, the compound “runner-up” consists of two independent words, “runner” and “up.”

NoteEven words where the prefix is written with a hyphen (e.g., “pre-approve,” “anti-glare”) are normally considered to be complex words rather than compound words, because the prefixes (“pre,” “anti”) cannot stand alone as words in their own right.

Worksheet: Compound words

Want to test your understanding of compound words? Check out the worksheet below. Try to find and highlight all the compound words in each sentence.

  1. My mother-in-law remembers watching the moon landing on television in her teenage years.
  2. We ate ice cream after the football game at the local high school.
  3. A high-profile case is being considered at the courthouse.
  4. A cat burglar has outpaced the night watchman and stolen the crown jewels!
  5. After he was knocked out, it was several minutes before the prizefighter came to.
  1. My mother-in-law remembers watching the moon landing on television in her teenage years.
    • This sentence contains all three kinds of compounds. “Mother-in-law” is a hyphenated compound noun. “Moon landing” is an open compound noun. And “teenage” (“teen” + “age”) is a closed compound adjective.
  1. We ate ice cream after the football game at the local high school.
    • This sentence contains three open compounds, all of them nouns: “ice cream,” “football game,” and “high school.” Additionally, “football” is itself a closed compound formed with “foot” and “ball.”
  1. A high-profile case is being considered at the courthouse.
    • This sentence contains two compound words: the hyphenated compound adjective “high-profile” and the closed compound noun “courthouse” (“court” + “house”).
  1. A cat burglar has outpaced the night watchman and stolen the crown jewels!
    • This sentence contains three open compound nouns—”cat burglar,” “night watchman,” and “crown jewels”—and the closed compound verb “outpaced. ” Moreover, “watchman” is itself a closed compound of “watch” and “man.”
  1. After he was knocked out, it was several minutes for the prizefighter to come to.
    • This sentence contains the open compound verbs (aka phrasal verbs) “knocked out” and “come to” and the closed compound noun “prizefighter” (“prize” + “fighter”).

Other interesting articles

If you want to know more about nouns, pronouns, verbs, and other parts of speech, make sure to check out some of our other language articles with explanations and examples.

Frequently asked questions about compound words

Is “today” a compound word?

Yes, today is a compound word, but a very old one. It wasn’t originally formed from the preposition “to” and the noun “day”; rather, it originates from their Old English equivalents, “tō” and “dæġe.”

In the past, it was sometimes written as a hyphenated compound: “to-day.” But the hyphen is no longer included; it’s always “today” now (“to day” is also wrong).

Is “because” a compound word?

Yes, the conjunction because is a compound word, but one with a long history. It originates in Middle English from the preposition “bi” (“by”) and the noun “cause.” Over time, the open compound “bi cause” became the closed compound “because,” which we use today.

Though it’s spelled this way now, the verb “be” is not one of the words that makes up “because.”

Sources in this article

We strongly encourage students to use sources in their work. You can cite our article (APA Style) or take a deep dive into the articles below.

This Scribbr article

Caulfield, J.
(2023, July 03). Compound Words | Types, List & Definition. Scribbr.
Retrieved July 19, 2023,
from https://www.scribbr.com/language-rules/compound-words/

Cite this article

Sources

Aarts, B. (2011). Oxford modern English grammar. Oxford University Press.

Butterfield, J. (Ed.). (2015). Fowler’s dictionary of modern English usage (4th ed.). Oxford University Press.