Waterproof Means Tested Against Water, Not Sealed From It
Proof is evidence that establishes truth. The suffix in waterproof and bulletproof carries the older sense of having withstood a test.
Proof is evidence sufficient to establish a fact. The suffix in *waterproof*, *bulletproof* and *foolproof* keeps a sense English otherwise lost: proof as *having withstood the test*. Armour that was bulletproof had literally been shot at to prove it. The same idea survives in *the proof of the pudding is in the eating* — the pudding's test is being eaten, not some abstract demonstration. *Proof* in spirits measures alcohol content, from a gunpowder test that proved a spirit strong enough.
- Evidence of truth. *Proof of purchase.*
- A trial print. *A proof copy.*
- Alcohol strength. *80 proof.*
- Resistant to. *Waterproof.*
- Latin — *probare*, to test. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | proof | The proof. |
| Verb | prove | Prove it. |
| Past | proved / proven | Proven. |
| Suffix | -proof | Fireproof. |
| Latin | probare | To test. |
- There is no proof either way.Evidence.
- The jacket is waterproof.Resistant.
- The whisky is 80 proof.Spirits.
Where proof means tested
- Bulletproof — originally armour actually shot at to prove it
- Waterproof — proved against water
- Foolproof — proof even against a foolish user
- Proof spirit — a strength tested by whether it would ignite gunpowder
- Proofread — to check a trial print before publication
Old French *prueve*, from Late Latin *proba*, a test, from *probare*, to prove.
Why does bulletproof end in proof?
Because armour was tested by shooting at it. Proof there means having withstood the test, not being sealed.
What does 80 proof mean?
A measure of alcoholic strength, from an old test of whether a spirit-soaked gunpowder charge would still ignite.