Hyphens in compound nouns


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For things that are described using two words (e.g., cooking-oil), there is sometimes a requirement to use a hyphen to eliminate ambiguity.

Use a Hyphen to Eliminate Ambiguity

There are no specific rules on forming compound nouns. For example, 'Ink-well' can be also be written 'ink well' or 'inkwell' - all are correct spellings. However, you should use a hyphen to eliminate ambiguity. Ambiguity is particularly prevalent when the first word of the pairing is a substance (like 'water' or 'ink').

Examples:

water-bottle / water bottle

(When the first word is a substance, a hyphen is used to show that the item is
not made of that substance.)

ice-axe / ice axe

(Both are acceptable, but 'ice-axe' makes it clear that the axe is not made of ice.)

paper-clip / paper clip / paperclip

(All 3 are acceptable. However, if the clip were made of paper, then only
'paper clip' could be used.)

Please could you pass me that plastic wire-fastener?

(a fastener made of plastic, i.e., not wire)

There is also some ambiguity when the first word of the pairing ends 'ing'. (This is called a present participle.)

Examples:

changing-room / changing room

(Both are acceptable, but 'changing-room' makes it clear that the room is not
changing.)

laughing-gas / laughing gas

(Both are acceptable, but 'laughing-gas' makes it clear that the gas is not
laughing.)

COMPOUND NOUN?

A single noun that comprises two or more words is called a 'compound noun'. Sometimes the words in a compound noun are joined together by a hyphen or hyphens. (e.g., water-bottle) (See lesson Types of Nouns.)

NOT ALL HAVE A ONE-WORD VERSION

Be aware that not all compound nouns have a one-word version. Even though 'inkwell' and 'paperclip' are fine, 'iceaxe' and 'waterbottle' are spelling mistakes. There are no rules governing this - you have to know.