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B1 – C1

Compound Nouns & Adjectives: The Complete Guide

Everything you need to build and correctly hyphenate compound nouns and adjectives in English, with the key before/after-noun rule and exam practice.

📖 Reading time: ~10 minutes ✅ Reviewed by a CELTA-qualified teacher 🎯 Covers A1 to B2

📋 What's in This Guide

  1. 1. Introduction — Building New Words From Two
  2. 2. Quick Summary
  3. 3. Compound Nouns
  4. 4. One Word, Two Words, or Hyphenated?
  5. 5. Compound Adjectives
  6. 6. The Key Hyphenation Rule
  7. 7. Common Mistakes
  8. 8. Exercises
  9. 9. Mini Quiz
  10. 10. Exam Focus — Cambridge, IELTS, SELT
  11. 11. Frequently Asked Questions
  12. 12. Related Grammar Guides
  13. 13. Book a Free Level Test

1. Introduction — Building New Words From Two

English constantly combines two or more words into a single new unit: "toothbrush," "well-known," "five-year-old." These are compound nouns and compound adjectives, and while the underlying pattern is simple, two words joining to create one meaning, the spelling conventions (one word? two words? hyphenated?) are genuinely inconsistent, and one specific hyphenation rule for compound adjectives is heavily tested at B2+ level.

2. Quick Summary

⚡ Compound Nouns & Adjectives at a Glance

Compound nounTwo words forming one thing: toothbrush, bus stop, mother-in-law
Compound adjectiveTwo or more words working as one adjective before a noun: a well-known author
Key RuleCompound adjectives before a noun are hyphenated; number + unit compounds don't pluralise
Common Mistake"a five-years-old boy" instead of "a five-year-old boy" (no plural inside the compound)
🇪🇸
Resumen en español Cuando un adjetivo compuesto con número va antes de un sustantivo, se escribe con guion y el sustantivo interno NO se pluraliza: "a five-year-old boy" (no "five-years-old"), aunque el niño tenga cinco años. El español no tiene esta regla de "despluralización" en compuestos, así que es un error muy común.

3. Compound Nouns

A compound noun combines two words (usually noun+noun, or adjective+noun) into a single naming unit for a specific thing.

TypeExamples
noun + nountoothbrush, bus stop, football, headache
adjective + nounblackboard, full moon, greenhouse
verb + nounswimming pool, washing machine, driving licence
noun + verb-ingsunrise, haircut

4. One Word, Two Words, or Hyphenated?

There's no fully reliable rule for this, English compound nouns settle into their spelling over time through common usage, and the same compound can even be spelled differently in different dictionaries. That said, some general patterns help.

PatternExamples
One word (older, very established compounds)toothbrush, bedroom, football, notebook
Two separate words (newer or less fused compounds)bus stop, remote control, coffee table
Hyphenated (a middle stage, or specific fixed compounds)mother-in-law, well-being, check-in
💡
When in doubt, check a dictionary Because this genuinely isn't fully predictable, even confident English speakers check a dictionary for less common compounds. Don't treat a wrong guess here as a major error, it's a spelling convention issue, not a grammar rule you've broken.

5. Compound Adjectives

A compound adjective combines two or more words to describe a noun as a single descriptive unit, and unlike compound nouns, these follow a genuinely reliable, testable spelling rule.

PatternExample
adjective + noun-eda blue-eyed cat, a good-natured person
number + nouna five-year-old boy, a three-bedroom flat
adjective + present participlea fast-moving vehicle, an easy-going manager
adjective + past participlea well-known author, a broken-hearted fan
noun + adjectivea world-famous singer, a duty-free shop

6. The Key Hyphenation Rule

This is the single most testable point in this whole topic: a compound adjective is hyphenated when it comes before the noun it describes, but usually written as separate words when it comes after the noun (after a linking verb like "be").

PositionExample
Before the noun, hyphenatedIt was a well-known problem.
After the noun/linking verb, not hyphenatedThe problem was well known.
Before the noun, hyphenatedShe's a five-year-old girl.
After, not hyphenated (and the number stays singular)The girl is five years old.
⚠️
Numbers inside compound adjectives never pluralise "A five-year-old boy," never "a five-years-old boy," even though the boy is five YEARS old. Once the number becomes part of a compound adjective before a noun, the unit word (year, not years) stays singular.

7. Common Mistakes

❌ Incorrect✅ CorrectWhy
a five-years-old boya five-year-old boyThe unit word inside a compound adjective never pluralises.
a well known author (before the noun)a well-known authorCompound adjectives before a noun need a hyphen.
The author is well-known. (after a linking verb)The author is well known.After a linking verb, the hyphen is usually dropped.
a three-bedrooms flata three-bedroom flatThe unit word (bedroom) stays singular inside the compound.

8. Exercises

A. Gap Fill — Complete with the correct compound form (8 questions)

1. She has a ___ (five / year / old) daughter.
2. The bridge is ___ (well / know) for its unusual design. (after linking verb, no hyphen)
3. It was a ___ (well / know) landmark. (before noun, hyphenated)
4. We stayed in a ___ (three / bedroom) apartment.
5. He's a ___ (fast / move) target, hard to catch.
6. The team's plan was ___ (well / think) out. (after linking verb)
7. That was a ___ (well / think) out plan. (before noun)
8. The child is ___ (ten / year) old.
Show Answers (A)
1. five-year-old   2. well known   3. well-known   4. three-bedroom   5. fast-moving   6. well thought   7. well-thought   8. ten years

B. Multiple Choice (5 questions)

1. She has a ___ daughter. (a) five-years-old (b) five-year-old
2. The plan is ___. (after linking verb) (a) well-known (b) well known
3. It was a ___ decision. (before noun) (a) well-known (b) well known
4. We live in a ___ house. (a) three-bedrooms (b) three-bedroom
5. He's a ___ worker. (a) hard-working (b) hard working
Show Answers (B)
1.b 2.b 3.a 4.b 5.a

C. Error Correction (4 questions)

1. a five-years-old boy
2. a well known author (before the noun)
3. The author is well-known. (after a linking verb)
4. a three-bedrooms flat
Show Answers (C)
1. a five-year-old boy
2. a well-known author
3. The author is well known.
4. a three-bedroom flat

D. Freer Practice — Write Your Own Sentences (2 tasks)

1. Write a sentence using a number + unit compound adjective before a noun (e.g. "a two-hour meeting").
2. Write a sentence with a compound adjective before a noun, then rewrite it after a linking verb without the hyphen.
Show Answers (D)
Model answers will vary. Examples:
1. "We sat through a two-hour meeting."
2. "It was a well-written essay." → "The essay was well written."

9. Mini Quiz

1. She has a ___ son.

2. It was a ___ decision.

3. The decision was ___.

4. We stayed in a ___ hotel.

10. Exam Focus — Cambridge, IELTS, SELT

ExamHow This Is TestedSample Question
Cambridge B2 First / C1 AdvancedCompound adjective hyphenation is a common Use of English and Writing accuracy point."a ___ (five/year) old child" (five-year-old)
IELTS WritingCorrect compound adjective formation before nouns is expected at higher bands for range and accuracy.Describing data with compound adjectives: "a fast-growing trend."
Trinity GESE/ISE (SELT)Age and duration compound adjectives come up constantly describing family and daily life."I have a three-year-old son."

11. Frequently Asked Questions

Two or more words combined into a single naming unit for a specific thing, such as toothbrush, bus stop or mother-in-law.
No fully reliable rule exists, this settles through common usage over time, so checking a dictionary for less familiar compounds is normal, even for native speakers.
Hyphenate the compound adjective when it comes before the noun it describes (a well-known author); it's usually written without a hyphen after a linking verb (the author is well known).
The unit word inside a number + unit compound adjective never takes a plural -s, even though the underlying fact (five years) is plural.
Usually, yes, for most descriptive compound adjectives, though some fixed, well-established compounds keep their hyphen in both positions.
Yes — age and duration compound adjectives (a five-year-old daughter, a two-hour journey) come up constantly describing family and daily life.
Adjective OrderHow compound adjectives fit into the wider order Word FormationPrefixes and suffixes, another word-building system -ed vs -ing AdjectivesAnother common adjective-formation pattern General English CoursesBuild every grammar point with expert guidance

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Compound nouns vs compound adjectives

Compound noun

Two or more words act as a noun: bus stop, website, swimming pool. Spelling can be open, closed or hyphenated.

Compound adjective

Words combine to modify a noun: a well-known actor, a ten-minute break.

Key hyphen rule

Hyphenation often clarifies a compound adjective before a noun. After a linking verb, many compounds are written without that attributive hyphen.

Compare

“It is a five-year course.” Notice that year stays singular inside the compound adjective.

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