One of the most common errors I see in manuscripts is unhyphenated compound adjectives. It’s not surprising – adjectives with two or more words are slippery little beasts. They can be closed (e.g. overtake), open (e.g. high stakes) or hyphenated (e.g. hard-working).
So how do you know the difference? And does it even matter? In this article, I explain what compound adjectives are and how to handle them like a pro.
What is a compound adjective?
Compound adjectives are adjectives that contain two or more words. Like single adjectives, they describe or modify a word, usually a noun. Compound adjectives can appear before the noun (known as attributive) or after the noun (known as predicative). For example, 'Skydiving is a high-risk sport' or 'Skydiving is high-risk'.
Types of compound adjectives
Compound adjectives can be structured in different ways. You can have an adjective paired with a noun, or an adverb paired with a past participle. Here's a chart with some common pairings:
When do you hyphenate compound adjectives?
Knowing when to hyphenate a compound adjective is where most writers slip up. In general, compound adjectives are hyphenated when they appear before a noun. This turns them into one descriptive unit. For example:
📌 Ten-hour journey
📌 Lead-generation machine
📌 Done-for-you copy
📌 Well-known author
📌 Five-year-old daughter
If the compound adjective is placed after a noun, hyphens are not usually required. For example:
📌 The author was well known.
📌 Her daughter was five years old.
However, some compound adjectives are always hyphenated, no matter where you put them. This will depend on your dictionary or style manual. Here are some examples:
📌 The building was state-of-the-art.
📌 John was absent-minded.
If a compound adjective includes an adverb that ends in ‘-ly’, you don’t need a hyphen. For example:
📌 Grammatically correct sentence
📌 Thinly veiled threat
What happens if you don’t hyphenate a compound adjective?
If you don’t use hyphenate correctly, it may confuse or slow down readers. In some cases, it could even convey the wrong message. Take a look at this example:
📌 He was a French stamp collector.
📌 He was French-stamp collector.
If the stamp collector is French, you don’t need a hyphen. If the collector collects French stamps, you do! See how a simple hyphen can change your meaning?
Top tip: Some closed compound adjectives can be mistaken for hyphenated compound adjectives. These include words like ‘undercooked’ (under-cooked), ‘cybersecurity’ (cyber-security) or ‘cooperate’ (co-operate). Always check your dictionary or style manual to make sure your spelling is correct.
To hyphenate or not to hyphenate …
As you can see, compound adjectives can be tricky, which is why so many writers get them wrong. Most need hyphens, but not always. It all depends on where they fall in the sentence and whether the compounds are open or closed.
If you forget, review the rules above – and keep a dictionary at hand. It's the best way to avoid ambiguity and improve readability.
For more tips on writing well, see Punctuation tip #1: Commas after introductory clauses and What's a comma splice (and when can you use it)?
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