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Using Hyphens in Compound Adjectives

The Quick Answer
You can use a hyphen (or hyphens) to link the words in a compound adjective to show it is a single adjective. (A compound adjective is a single adjective that is made up of more than one word.) For example:
  • two-seater aircraft
  • never-to-be-forgotten experience

What Is a Compound Adjective?

A single adjective made up of two or more words is called a compound adjective. The words in a compound adjective can be linked together by a hyphen (or hyphens) to show they are part of the same adjective.

In the UK, your readers will expect you to use hyphens in compound adjectives.

In the US, your readers will be more lenient. The US guidance is as follows:
Use a hyphen if it eliminates ambiguity or helps your reader. If you're unsure, use a hyphen.

The Hyphen Might Be Essential

Sometimes, a hyphen is essential to avoid ambiguity. Look at these examples:
  • a heavy-metal detector
  • a heavy metal detector
Both versions above are correct, but they mean different things. The first device detects heavy metals. The second device detects metal, and the device is heavy. If we're talking about a device that detects heavy metals, then putting heavy metal detector would be wrong in the UK and the US.

Compound Adjectives with Numbers

The easiest compound adjectives to spot are the ones that include numbers. For example:
  • Two-seater aircraft
  • 4-bedroom house

"24-hour" (This is correct.)

"3-day" (This is correct.)

  • Three stone weakling
  • (Three-stone would be better.)
  • 15-page document

Compound Adjectives Without Numbers

Lots of compound adjectives do not include numbers. For example:
  • Philip is a far-too-chatty individual.
  • That was a never-to-be-forgotten experience.
  • James is a second rate plumber.

This should be should be "8-week money-back guarantee".


"Cambridge-based" and "high-speed" (both correct)

Often, a compound adjective consists of words that would not normally be joined together with a hyphen. For example:
  • The double glazing is still leaking. Can you call that double-glazing salesman?
  • (The words double glazing only need a hyphen when they are functioning as an adjective. In this example, the first time they are used, they are not an adjective. The second time they are used, they are an adjective describing salesman.)

  • You call this silver service? She's not a trained silver-service waitress.
  • (The second time they are used, the words silver service describe waitress. As they are a compound adjective, they are linked with a hyphen to show they are a single adjective.)
Note

What Is an Adjective?

An adjective is a describing word (e.g., red, big, beautiful, contagious).

Read more about adjectives.

What Is a Compound Adjective?

A single adjective made up of two or more words is called a compound adjective. The words in a compound adjective are often linked together by a hyphen (or hyphens) to show that they are part of the same adjective. For example (compound adjectives shaded):
  • three-page document
  • ironing-board cover
Read more about compound adjectives.

Beware

More Than One Adjective or a Compound Adjective?

Do not be tempted to string all adjectives together with hyphens. It is common to use more than one adjective to describe something. When you use 2 or more adjectives to describe one thing, it is called enumeration of adjectives. For example:
  • A big maroon car
  • (Here, big and maroon are standalone adjectives. This is an example of enumeration of adjectives. There is no compound adjective.)
  • She is an intelligent articulate lady.
  • (Here, intelligent and articulate are standalone adjectives. This is an example of enumeration of adjectives. There is no compound adjective.)

Adverbs with Adjectives

Adjectives are often preceded by adverbs (e.g., very, well, beautifully, extremely).

Usually, there is no need to link an adverb to an adjective using a hyphen. For example:
  • Young Paula is a very talented student.
  • (As very is an adverb, it should not be linked to the adjective talented with a hyphen.)
Linking an adverb like very, most, or least to an adjective with a hyphen is an uncommon error. However, when an adverb ends in -ly (and lots do), some writers feel the urge to link it to the adjective with a hyphen. There is no need.
  • It is a wonderfully-decorated tree.
  • (The adverb wonderfully modifies the adjective decorated, but there is no need to join the two with a hyphen.)
However, with words like well, fast, and best (which are both adjectives and adverbs), a hyphen can be used to avoid ambiguity.
  • Alan is the best-known player on the pitch.
  • (In this example, Alan is known better than any other player.)

  • Alan is the best known player on the pitch.
  • (This example could be taken to mean the same as the one above or it could be taken to mean that Alan is the best player of all the known players on the pitch. The hyphen eliminates ambiguity.)
Top Tip

How To Spot a Compound Adjective

Put and between the adjectives. If there is no loss of meaning, then you are very likely dealing with several adjectives as opposed to a compound adjective. Let's try it:

step 1 large proud rooster
step 2 large and proud rooster

Although different in style, there is no loss of meaning. This is an example of two adjectives. Therefore, no hyphen is required.

step 1 free range rooster
step 2 free and range rooster  

In this example, there is a change in meaning. The rooster is not free and what is a range rooster? This is a compound adjective and should be written as free-range rooster.

step 1 first aid post
step 2 first and aid post

Although aid post is okay, there is a change in meaning with first post. This should be written as first-aid post.