proof

Etymology

From Middle English proof, from Old French prove, from Late Latin proba (“a proof”), from Latin probare (“to prove”); see prove; compare also the doublet probe.

noun

1. (countable) An effort, process, or operation designed to establish or discover a fact or truth; an act of testing; a test; a trial.
   1591, Edmund Spenser, Prosopopoia: or, Mother Hubbard's Tale, later also published in William Michael Rossetti, Humorous Poems, But the false Fox most kindly played his part, For whatsoever mother-wit or art Could work he put in proof. No practice sly, No counterpoint of cunning policy, No reach, no breach, that might him profit bring. But he the same did to his purpose wring.
   France I more praise and love; you are, my lord, Yourself for horsemanship much famed; and there You shall have many proofs to shew your skill. c. 1633, John Ford, Love's Sacrifice, Act 1, Scene 1
   A given quantity of the spirits was poured upon a quantity of gunpowder in a dish and set on fire. If at the end of the combustion, the gunpowder continued dry enough, it took fire and exploded; but if it had been wetted by the water in the spirits, the flame of the alcohol went out without setting the powder on fire. This was called the proof. 1831, Thomas Thomson, A System of Chemistry of Inorganic Bodies, volume 2
2. (uncountable) The degree of evidence which convinces the mind of any truth or fact, and produces belief; a test by facts or arguments which induce, or tend to induce, certainty of the judgment; conclusive evidence; demonstration.
   It was a grand sentence of Emanuel Swedenborg, which would alone indicate the greatness of that man's perception, — "It is no proof of a man's understanding to be able to confirm whatever he pleases; but to be able to discern that what is true is true, and that what is false is false, this is the mark and character of intelligence." 1841, Ralph Waldo Emerson, “The Over-Soul”, in Essays: First Series
   Faith, faith is an island in the setting sun But proof, yes Proof is the bottom line for everyone October 16 1990, Paul Simon, “Proof”, in The Rhythm of the Saints, Warner Bros.
3. The quality or state of having been proved or tried; firmness or hardness which resists impression, or does not yield to force; impenetrability of physical bodies.
4. (obsolete) Experience of something.
5. (uncountable, obsolete) Firmness of mind; stability not to be shaken.
6. (countable, printing) A proof sheet; a trial impression, as from type, taken for correction or examination.
   And these men scour the printed proof for error, blunder, and misspelling. 2010, Andrea Levy, The Long Song, Tinder Press (2017), page 382
7. (numismatics) A limited-run high-quality strike of a particular coin, originally as a test run, although nowadays mostly for collectors' sets.
8. (countable, logic, mathematics) A sequence of statements consisting of axioms, assumptions, statements already demonstrated in another proof, and statements that logically follow from previous statements in the sequence, and which concludes with a statement that is the object of the proof.
9. (countable, mathematics) A process for testing the accuracy of an operation performed. Compare prove, transitive verb, 5.
10. (obsolete) Armour of excellent or tried quality, and deemed impenetrable; properly, armour of proof.
11. (US) A measure of the alcohol content of liquor. Originally, in Britain, 100 proof was defined as 57.1% by volume (no longer used). In the US, 100 proof means that the alcohol content is 50% of the total volume of the liquid; thus, absolute alcohol would be 200 proof.

adj

1. Used in proving or testing.
   a proof load; a proof charge
2. Firm or successful in resisting.
   proof against harm
   waterproof; bombproof
   This was a good, ſtout proof article of faith, pronounced under an anathema, by the venerable fathers of this philoſophick ſynod. 1790, Edmund Burke, “Reflections on the Revolution in France”, in The Works of The Right Honourable Edmund Burke, volume 5, published 1803, page 426
   quoted in 1818, Christopher Kelly, History of the French Revolution and of the Wars produced by that Memorable Event The French cavalry, in proof armour, repeatedly charged our squares, their cannon opening chasms; but the British infantry, though greatly diminished, were inflexible and impenetrable to the last.
3. (of alcoholic liquors) Being of a certain standard as to alcohol content.
   60% proof liquor

verb

1. (transitive, intransitive, colloquial) To proofread.
2. (transitive) To make resistant, especially to water.
3. (transitive, firearms) To test-fire with a load considerably more powerful than the firearm in question's rated maximum chamber pressure, in order to establish the firearm's ability to withstand pressures well in excess of those expected in service without bursting.
4. (transitive, cooking) To allow yeast-containing dough to rise.
5. (transitive, cooking) To test the activeness of yeast.