I am always confused when using a noun and a gerund as an adjective

For example, do we say swim clothing or swimming clothing, electric generator or electricity generator?

  • There's no general rule for idiomatic expressions (swim suit, electrical generator, carving knife).
    – John Feltz
    Commented Jan 16, 2017 at 13:28
  • The first two should be hyphenated, "swim-clothing / swimming-clothing". They are compound nouns - single words - so there's no modifiers involved. In "electric generator" and "electricity generator", "electric" and "electricity" are both nominals, not adjectives, modifying "generator". Incidentally, it is far more natural to use one of the compounds "swim-suit" or "swim-wear", than the two examples you gave,
    – BillJ
    Commented Jan 16, 2017 at 16:31

1 Answer 1


As John Feltz mentions, most of these are idiomatic and each may be constructed differently. You may just have to memorize the words as individual vocabulary, as you come across them. The two you mention should be:


electric generator.

Again, there is no consistent pattern. For example, we say today is a "work day" (a day when most people work), but two people are a "working couple" (both of them work). You can "lend" someone a "helping hand", but you give them "helpful advice". And so on.

By the way, be careful of some resources online that offer lists of these things. In the hope of providing a reference I came across this site, but it is full of errors.

  • @BillJ what term is appropriate then for phrases and compounds that commonly appear in a particular way that is not deducible from common grammar -- for example, why is it "swimwear" and never "swimming clothing"? I'm honestly curious to know so I can use the right term. Thanks!
    – Andrew
    Commented Jan 16, 2017 at 19:04
  • 1
    You could call them idiomatic. They're not idioms since the meaning is easily deduced from the component parts. Some people talk of words or expressions being "natural" or otherwise. Neither "swim clothing" nor "swimming clothing" are idiomatic; instead we say "swim-wear" (or "swimwear") or possibly "swimsuit" or "swimming-costume".
    – BillJ
    Commented Jan 17, 2017 at 9:33

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