Compound Nouns

Compound Nouns

A compound noun is a noun made from at least two words. There are three forms for compound nouns: (1) with spaces, (2) without spaces and (3) with hyphens.

Easy Examples of Compound Nouns

  • swimming pool, grey matter, fish tank
  • (with spaces)
  • shotgun, housework, eyelid
  • (without spaces)
  • baby-sitter, laughing-gas, daughter-in-law
  • (with hyphens)

Real-Life Examples of Compound Nouns

  • Whenever the lion fish in the fish tank in the captain's ready room died, it was always a sad moment. (Patrick Stewart, Star Trek's Jean Luke Picard)
  • Polygraph tests are 20th-century witchcraft. (US politician Sam Ervin)
  • Those you helped will remember you when the forget-me-nots have withered. (Preacher Charles Spurgeon)
Most compound nouns are made up with the following components:
  • noun + noun: Bath tub, seaman, wall-paper
  • adjective + noun: full moon, highway, whiteboard
Other common combinations include:
  • verb + noun: washing machine, driving licence, breakfast
  • noun + verb: sunrise, rainfall, haircut
  • preposition (adverb) + noun: influx, onlooker, bystander
  • preposition (adverb) + verb: output, input, overthrow
  • verb + preposition (adverb): checkout, take-off, drawback

Why Should I Care about Compound Nouns?

There are three key issues related to compound nouns.

(1) Choosing the correct version (i.e., the version with spaces, nothing or hyphens)

Choosing the right or best form of a compound noun can be a nightmare. Here's the situation:
  • Some compound nouns were always the one-word version (e.g., keyboard)
  • Some two-word ones have transitioned to a one-word version (e.g., snow man to snowman)
  • Some two-word ones are transitioning to a one-word version (e.g., eye opener to eyeopener).
  • Some two-word ones are not transitioning (e.g., peace pipe)
  • Some compound nouns were always the hyphenated version (e.g., self-control).
  • Some two-word ones have transitioned to a hyphenated version (e.g., play off to play-off and soon playoff).
  • Some two-word ones are transitioning to a hyphenated version (e.g., ice cream to ice-cream).
  • Some exist in two versions (e.g., ice-axe or ice axe but not iceaxe)
  • Some exist in all three versions (e.g., chatroom, chat-room, chat room )
To give yourself the best chance of hitting the right or best version, go through the following checks.

(Check 1) Check if the one-word version exists using your spellchecker or a dictionary. If it does, then happy days you're done. If it doesn't, go to Check 2.

(Check 2) Check if the hyphenated version exists using a dictionary. (You can't use your spellchecker because it will treat the hyphen like a space, check the spelling of the sub-words either side and trust that you know what you're doing with compound nouns. Yeah, thanks for that, Microsoft.) If it does exist, you're done. If it doesn't, do Check 3, 4 and 5.

Here's some guidance on the types of compound nouns that should always be hyphenated:
  • A noun in the form "role"-"role" (e.g., student-athlete, soldier-poet, boy-child)
  • Nouns with a preposition in the middle (e.g., man-of-war, brothers-in-arms)
  • Titles of relatives with great (e.g., great-grandmother, great-great-grandson)
  • Fractions written in full (e.g., two-thirds, one-quarter)
  • Titles with vice and elect (e.g., president-elect, vice-chair)
  • Words with self (e.g., self-awareness, self-restraint)
  • (The entry on prefixes gives guidance on hyphenation too.)
(Check 3) You're now left with the two-word version, which you should use unless it makes your sentence ambiguous.
  • I like braising steak.
  • (This could be a comment about how you like to cook steak, so write braising-steak to eliminate the ambiguity.)
  • I need a wire fastener.
  • (This could be construed as fastener made of wire, so write wire-fastener to eliminate the ambiguity.)
(Check 4) If there was no ambiguity, then you're still left with the two-word version, which you should use unless you feel the urge to hyphenate it so your readers can spot it as a single entity in a flash.
  • The overwhelming challenge initially is getting to positive cash-flow. (Businessman John Mackey)
  • I actually have this fantasy of giving up my cell-phone. (Actress Julia Stiles)
  • Domain names and websites are the new real-estate. (Entrepreneur Marc Ostrofsky)
The hyphenated versions stand out as single entities, making them easier to read. That's the justification.

By hyphenating a two-word compound noun, you're contributing to its transition to the hyphenated version and even the one-word version. Be aware that even though your intent might be to make your readers' absorption of your words easier for them, you are running the risk of annoying some of them if you hyphenate a well-established two-worder.

(Check 5) If you've put a hyphen in your compound noun to make it stand out more clearly as a single entity, think about that decision again. Still happy? Then go for it.

(2) Forming the plural of a compound noun.

Compound nouns with hyphens (e.g., brother-in-law) and compound nouns with spaces (e.g., Knight Templar) usually form their plurals by pluralising the principal word.
  • I used to have two brothers-in-law. One was a karate expert, who later joined the army. The first time he saluted, he killed himself. (Comedian Henny Youngman)
  • The Knights Templar were a sort of medieval SAS. (Historian Dan Jones)
When there is no obvious principal word, add s (or es) to the end of the compound (e.g., forget-me-nots)
  • Two lieutenant generals presided over the courts-martial. (There is ambiguity about the principal word in court-martial, but courts-martial is about twice as common as court-martials.)

    (3) Creating the possessive form of a compound noun like mother-in-law.

    With compound noun like mother-in-law, the possessive form is created by adding 's to the end, regardless of whether it is singular or plural.

    SingularPlural
    sister-in-law's carsisters-in-law's husbands
    colonel-in-chief's arrivalcolonels-in-chief's meeting
    maid of honour's bouquetmaids of honour's arrival

    Key Points

    • When writing a compound noun, use the one-word version if it exists. If it doesn't, use the hyphenated version if it exists. If it doesn't, use the two-word version, but consider the hyphenated version if it eliminates ambiguity or helps your readers.
    • Form the plural of a two-word or hyphenated compound noun by pluralising the principal word.
      • My brothers-in-law were both stung when the Portuguese men-of-war entered in the swimming area.
    • With a compound noun like mother-in-law, add 's to create the possessive form (regardless of whether it's singular or plural).
      • To protect her sister-in-law's business, she asked the bank to freeze her sons-in-law's bank accounts.
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