I was wondering if you combine any word and add "proof" at the and, does that automatically means that it is protected against the first word?

For example: Bulletproof - means something that can't be pierced by a bullet

But if I say: Catproof or Appleproof does that mean something that is protected against cats or apples?

Thank you

  • 2
    Yes, but consider using a hyphen to coin new compounds, such as "cat-proof." I'm not sure if appleproof would work, since it's not clear what you're proofing yourself against.
    – SEL
    Sep 30, 2014 at 23:49
  • 1
    @SEL you are not necessarily proofing yourself against cats or apples... But, anyway, I agree that apple-proof is rather hard to get hold of. Oh, I just thought of 'teacher.'
    – pazzo
    Oct 1, 2014 at 0:34
  • 4
    Those of us who live with cats know that there is no such thing as "cat-proof".
    – JenSCDC
    Oct 1, 2014 at 1:29
  • 'The point of productivity is not that you can add a suffix to any word you please, but that it can be added to some words to create new words. [Only if it cannot be added to any words in order to create new words is it said to be unproductive.]' [Cerberus; tweaked] Thus knife-proof has been used and should cause few concerns; but fork-proof, poniard-proof, epee-proof and halberd-proof seem extremely rare; glaves-proof vanishingly so. Wikipedia lists some (unhyphenated) words with the suffix proof. Oct 1, 2014 at 9:59
  • 2
    Then again, there is of course the Apple-Haken-proof of the four-colour-theorem, which does not denote that the theorem is protected against apples (or hakens). :) Oct 1, 2014 at 12:19

2 Answers 2


Yes, this is the normal way that compound words are formed. The second meaning of proof as defined by the online Merriam-Webster is

designed or made to prevent or protect against something harmful

So, yes, if you were to coin appleproof it would indeed be understood as something that is safe from apples. The only exception I know of is are numbers. Because of another meaning of the word proof, hundredproof would not mean "safe from hundreds" but 50% alcohol. From the same source:

b : strength with reference to the standard for proof spirit; specifically : alcoholic strength indicated by a number that is twice the percent by volume of alcohol present

  • As I understand it, the second meaning of "proof" comes from the British navy, where 100 Proof meant just enough concentration of alcohol to cause navy gunpowder to spontaneously combust, thus "proving" its potency. That strength was close to, and was later standardized to, 50 percent alcohol by volume.
    – keshlam
    Oct 1, 2014 at 0:48
  • 3
    @keshlam close, but not quite. Alcohol does not make gunpowder spontaneously combust, that would have been quite a trick. What you're referring to is the practice of whetting the gunpowder with alcohol and testing whether it could then be lit. If so, the alcohol was strong enough. See, for example, here.
    – terdon
    Oct 1, 2014 at 0:52
  • Ah. That does make more sense than the way I'd heard it. Correction appreciated! (It would be nice if the system didn't block editing of comments after 5 minutes... sigh.)
    – keshlam
    Oct 1, 2014 at 0:55
  • @keshlam please provide references for this type of claim. While prove did indeed mean test / try I can find no evidence that that was the sense used in the idiom. What makes you say so? Wikipedia traces it to the Latin phrase exceptio probat regulam in casibus non exceptis where probat is translated as confirms. How would "the exception tests the rule" make sense?
    – terdon
    Oct 1, 2014 at 0:59
  • 1
    @keshlam I looked into this a bit more and I see what you were getting at, that the exception tests whether the rule is true. That, however, is also a misunderstanding of the phrase.
    – terdon
    Oct 1, 2014 at 1:57

Yes, that would be the usual interpretation. Common example: "childproof" containers for medicines and other potentially dangerous things.

And those of us with cats are definitely familiar with the idea of trying to make things catproof; I need to keep the toilet paper covered when not in use or one of mine unrolls it.

  • And what needs to be apple-proof? A diabetic? I mean, I dunno, seriously. A window? Maybe an honest teacher?
    – pazzo
    Oct 1, 2014 at 0:35
  • 6
    A car windshield when parked under an apple tree? The fact that the term doesn't have a useful application doesn't make it meaningless, it just makes it useless.
    – keshlam
    Oct 1, 2014 at 0:44
  • Using Google Dictionary's first listed definition of word: word noun 1. a single distinct meaningful element of speech or writing [bolding mine] and its 'synonym: term', together with M-W's meaningful: ' having an assigned function in a language system' encourages me to argue that a 'useless word' is a contradiction in terms. Chambers (20th C Dictionary) once famously 'defined' mirbane as being 'an apparently meaningless word' but has since had the sense to drop that description. Oct 1, 2014 at 10:10
  • 1
    Right. The compound word "appleproof" does have a clear meaning, even if it's not one that we'd often need.
    – keshlam
    Oct 1, 2014 at 12:40

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