What are compound words in English?

Compound words are formed by combining two or more words to create a new word with a specific meaning. They can be written as one word (toothpaste, bedroom), two words (bus stop, ice cream), or with a hyphen (well-known, mother-in-law). The three main types are compound nouns, compound adjectives, and compound verbs.

How do you know when to use a hyphen in compound words?

The main rule is: compound adjectives are hyphenated BEFORE a noun (a well-known singer) but NOT after a verb (The singer is well known). Exceptions: self- compounds are always hyphenated (self-confident), number compounds are hyphenated before nouns (a five-star hotel), and -ly adverbs are NEVER hyphenated (a beautifully written poem, not beautifully-written).

What is the difference between compound nouns and compound adjectives?

Compound nouns name things (toothpaste, bus stop, mother-in-law) while compound adjectives describe things (well-known, old-fashioned, hard-working). Compound nouns can be one word, two words, or hyphenated. Compound adjectives are typically hyphenated when placed before a noun they modify.

Are compound verbs always written as one word?

Most compound verbs with prefixes like over-, under-, out-, up-, and down- are written as one word: overcome, understand, outperform, upgrade, download. However, some phrasal verbs that function as compound verbs may be written as two words when used as verbs (to break down) but one word as nouns (a breakdown).

How do you make compound nouns plural?

For most compound nouns, add -s to the end: toothbrushes, bedrooms, airports. For hyphenated compounds with a clear main noun, make that noun plural: mothers-in-law (not mother-in-laws), passers-by (not passer-bys), brothers-in-law. The main noun receives the plural marker.

What is the -ly adverb hyphenation exception?

Adverbs ending in -ly are NEVER hyphenated with the word that follows, even before a noun. Write "a beautifully written poem" (not "beautifully-written"), "a carefully planned event" (not "carefully-planned"), "a highly qualified candidate" (not "highly-qualified"). This is because -ly already signals that the word is an adverb, so a hyphen is unnecessary.

Compound Words Exercises - 180 Free Practice Questions with Answers

Compound Words

Master compound nouns, adjectives, verbs and hyphenation rules with 9 progressive exercises and 180 practice questions

Exercises

180

Questions

2-3h

Total Time

Compound words are formed when two or more existing words combine to create a new word with its own distinct meaning. They are one of the most productive ways English expands its vocabulary. The meaning of a compound is often more than the sum of its parts — a "greenhouse" is not simply a green house, and a "butterfly" has nothing to do with butter or flying.

doghouse

dog + house

post office

post + office

well-known

well + known

overcome

over + come

The Three Forms of Compound Words

Closed Compounds

Written as one word with no space or hyphen.

"toothpaste"
"bedroom"
"football"
"sunflower"

Open Compounds

Written as two separate words.

"bus stop"
"ice cream"
"high school"
"living room"

Hyphenated Compounds

Joined by a hyphen.

"well-known"
"mother-in-law"
"self-confident"
"old-fashioned"

Key insight: There is no single rule that determines whether a compound is closed, open, or hyphenated. The form depends on convention and evolves over time. For example, "e-mail" was originally hyphenated but is now commonly written as "email." When in doubt, always check a dictionary.

How Are Compound Nouns Formed?

Compound nouns are the most common type of compound word, accounting for roughly 70% of all compounds in English. They are formed by combining words in several different patterns, with the most frequent being noun + noun combinations. The stress pattern is important: compound nouns typically have primary stress on the first element ("BLACKboard" vs. "black BOARD").

toothpaste

noun + noun

sunlight

noun + noun

swimming pool

verb + noun

airport

noun + noun

Pattern	Examples	Frequency
Noun + Noun	toothpaste, bedroom, football	Most common
Adjective + Noun	greenhouse, software, blackboard	Very common
Verb + Noun	swimming pool, washing machine	Common
Verb + Preposition	breakdown, takeoff, checkout	Common
Noun + Prep + Noun	mother-in-law, commander-in-chief	Less common

Types of Compound Words - Nouns, Adjectives, and Verbs Explained

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How Do You Form Compound Adjectives?

Compound adjectives are formed by combining two or more words that together modify a noun. They are usually hyphenated when placed before the noun they describe. Understanding the formation patterns helps you recognise and create compound adjectives naturally.

Adjective + Past Participle

well-known, old-fashioned, narrow-minded, cold-hearted

Adjective + Present Participle

hard-working, good-looking, easy-going, long-lasting

Noun + Participle

time-consuming, mouth-watering, heart-breaking, sun-dried

Adjective + Noun + -ed

narrow-minded, cold-hearted, blue-eyed, left-handed

Number + Noun

five-star, three-bedroom, ten-minute, two-hour

Study tip: When a number compound is used before a noun, the noun stays singular: "a five-star hotel" (NOT "five-stars hotel"), "a ten-minute walk" (NOT "ten-minutes walk").

When Do You Hyphenate Compound Adjectives?

The key rule for compound adjective hyphenation depends on position. When a compound adjective appears before the noun it modifies, it is hyphenated. When it appears after a linking verb like "be," no hyphen is needed. However, there are important exceptions to learn.

Before a Noun (Hyphenated)	After a Verb (No Hyphen)
"a well-known singer"	"The singer is well known."
"an old-fashioned dress"	"That dress is old fashioned."
"a five-star hotel"	"The hotel is five star."

Important Exceptions

The -ly Exception

Never hyphenate adverbs ending in -ly: "a beautifully written poem" (NOT "beautifully-written").

Self- Always Hyphenated

Compounds with "self-" are always hyphenated regardless of position: "She is self-confident."

Number Compounds Before Nouns

Always hyphenated when modifying a noun: "a three-bedroom flat", "a 200-page book."

Compound Words Hyphenation Rules - When to Use Hyphens

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What Are Compound Verbs in English?

Compound verbs combine a prefix or another word with a verb to create a new meaning. The most productive prefixes for compound verbs are over-, under-, out-, up-, and down-. Unlike compound nouns and adjectives, compound verbs are usually written as one word without a hyphen.

Over- (too much / above)

overcome — to succeed despite difficulties
overlook — to fail to notice
overestimate — to think something is more than it is
overreact — to respond too strongly

Under- (not enough / below)

understand — to comprehend meaning
underestimate — to think something is less than it is
undergo — to experience or endure
undermine — to weaken gradually

Out- (surpass / beyond)

outperform — to do better than
outgrow — to grow too large for
outnumber — to be greater in number
outlive — to live longer than

Up- / Down- (direction / change)

upgrade — to improve quality
upload — to transfer data upward
download — to transfer data downward
downsize — to reduce in size

Verb vs. Noun Forms

Be careful: the verb and noun forms may differ in spelling and stress. The verb "to break down" (two words, stress on "down") becomes the noun "a breakdown" (one word, stress on "break"). Similarly: "to set up" → "a setup", "to take off" → "a takeoff."

How Do You Know If a Compound Is One Word, Two Words, or Hyphenated?

Unfortunately, there is no single reliable rule to determine the form of a compound word. English spelling of compounds is largely based on convention, and it varies between dictionaries and evolves over time. However, there are useful trends and guidelines that can help.

General Trends

Older, established compounds tend to be one word

"breakfast" (originally "break fast"), "cupboard" (originally "cup board"), "waistcoat."

Newer compounds often start as two words

"web page" (now often "webpage"), "e-mail" (now usually "email"). Over time, open compounds often become closed.

Compound adjectives before nouns are typically hyphenated

"a well-known actor", "a time-consuming task", "a five-year plan."

Use a dictionary when unsure

Cambridge, Oxford, and Merriam-Webster are all reliable references. Note that British and American English may differ.

The Lifecycle of a Compound Word

Many compounds follow a predictable lifecycle: they start as two words ("ice cream"), may become hyphenated ("e-mail"), and eventually merge into one word ("email"). This process can take decades or centuries. The more frequently a compound is used, the faster it tends to close up.

What Are the Most Common Compound Word Mistakes?

Analysis of learner corpora and Cambridge FCE exam data reveals five recurring categories of compound word errors. Understanding these patterns can help you avoid the most frequent mistakes and improve your accuracy significantly.

35%

Missing hyphens

before nouns

25%

Wrong spacing

open vs. closed

15%

-ly hyphenation

unnecessary hyphens

15%

Wrong word order

in compounds

10%

Incorrect plurals

of hyphenated words

Examples of Common Errors

Missing hyphen before a noun

✗ "a well known singer"→✓ "a well-known singer"

Hyphenating after -ly adverbs

✗ "a beautifully-written poem"→✓ "a beautifully written poem"

Wrong plural on hyphenated compounds

✗ "mother-in-laws"→✓ "mothers-in-law"

Wrong spacing (open vs. closed)

✗ "tooth paste" / "icecream"→✓ "toothpaste" / "ice cream"

How Are Compound Words Different from Word Formation?

Compound words and word formation (affixation) are both morphological processes that create new words, but they work differently. Compounds join two complete, independent words, while word formation adds prefixes or suffixes to word roots. Understanding the distinction helps with vocabulary building and exam preparation.

Feature	Compound Words	Word Formation (Affixation)
Process	Combines two complete words	Adds prefix/suffix to a root
Example	tooth + paste = toothpaste	un- + happy = unhappy
Components	Both parts can stand alone	Prefix/suffix cannot stand alone
Word class	May change (sun + flower = sunflower)	Often changes (happy → happiness)
Stress	Usually on first element	Varies by prefix/suffix

The Key Test

Can each part stand alone as a real word? If yes, it is a compound. "Tooth" and "paste" are both real words → "toothpaste" is a compound. "Un-" is not a real word on its own → "unhappy" is word formation, not a compound. Both processes are tested in Cambridge FCE and CAE Use of English papers.

Frequently Asked Questions

Sources

Statistics and research cited on this page:

•
Biber et al. (2021) - Longman Grammar of Spoken and Written English. Comprehensive corpus-based analysis of compound word formation patterns and frequency data across registers.
•
English Profile - CEFR word lists documenting which compound words appear at each proficiency level (A1–C2), used to calibrate exercise difficulty.englishprofile.org
•
Cambridge Assessment - FCE Use of English analysis showing compound word error patterns: 35% missing hyphens, 25% spacing errors, 15% -ly hyphenation, 15% word order, 10% plural formation.cambridgeenglish.org
•
Huddleston & Pullum (2002) - The Cambridge Grammar of the English Language. Definitive reference on compound word classification, hyphenation rules, and the distinction between compounds and affixed words.
•
British National Corpus - Distribution data showing approximately 70% of compound words are nouns, with noun+noun being the most productive pattern.natcorp.ox.ac.uk

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Compound Words Exercises - 180 Free Practice Questions with Answers

Compound Words

All 9 Exercises

Compound Adjectives — Easy

Compound Adjectives — Intermediate

Compound Adjectives — Advanced

Compound Nouns — Easy

Compound Nouns — Intermediate

Compound Nouns — Advanced

Compound Verbs

Hyphenation Rules

Mixed Compound Words

What Are Compound Words?

The Three Forms of Compound Words

Closed Compounds

Open Compounds

Hyphenated Compounds

How Are Compound Nouns Formed?

How Do You Form Compound Adjectives?

Adjective + Past Participle

Adjective + Present Participle

Noun + Participle

Adjective + Noun + -ed

Number + Noun

When Do You Hyphenate Compound Adjectives?

Important Exceptions

What Are Compound Verbs in English?

Over- (too much / above)

Under- (not enough / below)

Out- (surpass / beyond)

Up- / Down- (direction / change)

Verb vs. Noun Forms

How Do You Know If a Compound Is One Word, Two Words, or Hyphenated?

General Trends

The Lifecycle of a Compound Word

What Are the Most Common Compound Word Mistakes?

Examples of Common Errors

How Are Compound Words Different from Word Formation?

The Key Test

Frequently Asked Questions

What are compound words in English?

How do you know when to use a hyphen in compound words?

What is the difference between compound nouns and compound adjectives?

Are compound verbs always written as one word?

How do you make compound nouns plural?

What is the -ly adverb hyphenation exception?

Sources

Speaking Practice: Compound Words

Tips for Compound Words Discussion Practice

Free Downloads

Compound Words Infographics (2 Charts)

Worksheet (PDF)

Answer Key (PDF)

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