Compound nouns (i.e. compound words functioning as nouns) are the most common type of compound word. While compound nouns usually appear as one or two words (e.g. bookstore, notebook or moving box), in some instances they require a hyphen. While your main consideration when hyphenating is consistency, you are advised to refer to the appropriate style guide and dictionary for the situation in which you are writing for guidance.
If you are writing in an Australian university context, the most appropriate reference books for authors will often be the Style Manual and Macquarie Dictionary, although your department may have its own style preferences, and your field may follow yet other hyphenation preferences by convention. Whichever hyphenation choice you do make, applying that choice consistently is the most important thing.
The rules for the various types of compound nouns are covered below. The principles can be extended to new words not yet listed in dictionaries.
If you would like to watch an introductory video on compound words prior to reading this article, you can access one on our YouTube channel.
Verb + Adverb
A verb + adverb compound noun requires a hyphen (to show that the adverb is linked with the compound rather than the other elements of the sentence): march-by, sign-off, shake-out, stake-out, made-up.
Have you got the sign-off from the boss yet?
The Captain organised a march-by for the president’s inauguration.
Adverb + Verb
An adverb + verb compound noun appears as one word (i.e. does not require a hyphen): downpour, uproar, input.
The umpire’s decision provoked uproar from the crowd.
I value your input greatly.
Verb + Noun and Noun + Verb
Compound nouns formed by verb + noun or noun + verb do not require hyphens, unless the verb has a suffix: rattlesnake, roadblock, sunrise.
If an inflected verb appears as the first element, the result is presented as two words (i.e. no hyphen is required): flying saucer, washing machine, swimming pool.
If an inflected verb appears as the second element and the preceding noun is one syllable, the result is usually presented as one word (i.e. no hyphen is required): bookmaker, stocktaking.
If an inflected verb appears as the second element and is preceded by a noun of more than one syllable, the result is either hyphenated or presented as two words: cabinet-maker, boiler-maker, potato grower, wheat farmer. In this case, you will need to refer to your chosen dictionary to check whether a hyphen is needed.
Noun + Noun
Rules for hyphenation of noun + noun compound nouns vary greatly. Check your relevant style guide or dictionary . However, the following two rules are generally agreed upon across style guides and dictionaries.
Hyphenate expressions in which each element has equal status, and expressions in which the elements rhyme: owner-driver, city-state, philosopher-king, hocus-pocus.
Adjective + Noun
Compound nouns composed of an adjective followed by a noun are written as two words (i.e. not hyphenated): black market, red tape, free will.
The amount of red tape in the modern economy inadvertently supports a second economy in the form of the black market.
There are exceptions, including that some very common adjective + noun compound words are written as one word: blackboard, redhead. Check your relevant style guide or dictionary.
The teacher’s chalk screeched along the blackboard.
If an adjective + noun compound noun is further modified (e.g. by being placed before a noun to be used adjectively), a hyphen is be required: middle-class neighbourhood, high-quality boots, fire-proof jacket.
The firefighters requested that the city requisition additional fire-proof jackets.
Gerund + Noun
A gerund is a noun form that is derived from a verb: running, digging, standing.
When a gerund + noun compound noun is being used as a noun, no hyphen is needed: running shoes, standing desk.
However, if the gerund + noun compound noun is being used adjectivally (i.e. to describe another noun), a hyphen must be used: running-shoe sale, standing-desk box.
I was lucky enough to buy my new running shoes during a big running-shoe sale.
Noun + Gerund
If a noun + gerund compound noun is being used as a noun, no hyphen is needed: mountain climbing, mischief making.
However, when being used adjectivally (i.e. to describe another noun), a hyphen must be used: mountain-climbing enthusiast, mischief-making child.
He loves mountain climbing so much. He is a mountain-climbing enthusiast.
Some permanent compounds of this type are closed: bookkeeping, copyediting, caregiving. Check your relevant style guide or dictionary.
Noun + Numeral and Noun + Single Letter
Compound nouns formed by either a noun and a numeral, or a noun and a single letter, do not require a hyphen, regardless of whether they are being used as nouns or adjectivally: type A, type A executive, type 2 diabetes, size 11 shoes, a page one headline.
Authors writing in technical fields may encounter some exceptions to this rule, with some compound nouns inclusive of numerals or single letters having become hyphenated in those fields by convention. Please always defer to the preferences of the style guide or dictionary most appropriate for the situation in which you write.
Noun + Participle and Participle + Noun
Compound nouns comprised of a noun and a participle (in any order) must be hyphenated when being used as an adjective: a garden-filled city, cutting-edge methods. Otherwise, no hyphens are needed.
The garden-filled city of Toowoomba attracts many tourists. The many garden tours mean your days will be garden filled.
Noun Phrases
Rules for the hyphenation of noun phrases vary greatly. Check your relevant style guide or dictionary: stick-in-the-mud, jack-of-all-trades, a flash in the pan.
