Hyphens in Compound Nouns
The Quick AnswerA single noun made up of two or more words is called a compound noun (e.g., cooking-oil, pickpocket).
The rules on whether to put a hyphen, a space, or nothing between the words in a compound noun are inconsistent. For example:
- inkwell , ink well , ink-well
- iceaxe , ice axe , ice-axe
- waterbottle , water bottle , water-bottle
Inconsistency of Hyphens in Compound NounsA single noun made up of two or more words is called a compound noun (e.g., water-bottle, snowman). Compound nouns written as single words (e.g., snowman, pickpocket) do not cause writers many problems. However, a compound noun written as two or more words raises the question of whether those words should be linked with a hyphen(s).
Unfortunately, there are no specific rules on forming compound nouns. For example, ink-well can be written ink well or inkwell. All three versions are acceptable.
Use a Hyphen to Eliminate AmbiguityYou 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).
- water-bottle / water bottle (When the first word is a substance, a hyphen is useful to show 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, be aware that paper clip could be taken to mean a clip made of paper not a clip for paper.)
- Please pass me the wire-fastener? (This is a fastener for wire not necessarily made of wire.)
- 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.)