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See also: -proof, prof, and Prof.


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From Middle English proof, from Old French prove, from Late Latin proba (a proof), from Latin probare (to prove); see prove.



proof (countable and uncountable, plural proofs)

  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.
    • c. 1633, John Ford, Love's Sacrifice, Act 1, Scene 1,
      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.
    • 1831, Thomas Thomson, A System of Chemistry of Inorganic Bodies, Volume 2,
      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.
  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.
  3. The quality or state of having been proved or tried; firmness or hardness which resists impression, or doesn't yield to force; impenetrability of physical bodies.
  4. (obsolete) Experience of something.
    • 1590, Edmund Spenser, The Faerie Queene, III.1:
      But the chaste damzell, that had never priefe / Of such malengine and fine forgerye, / Did easely beleeve her strong extremitye.
  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.
  7. (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.
  8. (countable, mathematics) A process for testing the accuracy of an operation performed. Compare prove, transitive verb, 5.
  9. (obsolete) Armour of excellent or tried quality, and deemed impenetrable; properly, armour of proof.
  10. (US) A measure of the alcohol content of liquor. Originally, in Britain, 100 proof was defined as 57.1% by volume (not used anymore). In the US, 100 proof means that the alcohol content is 50% of the total volume of the liquid, and thus, absolute alcohol would be 200 proof.


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proof (comparative more proof, superlative most proof)

  1. Used in proving or testing.
    a proof load; a proof charge
  2. Firm or successful in resisting.
    proof against harm
    waterproof; bombproof.
    • 1671, John Milton, Paradise Regained, 1820, Dr Aiken (biographies), Select Works of the British Poets, page 125,
      And opportunity I here have had / To try thee, sift thee, and confess have found thee / Proof against all temptation as a rock / Of adamant, and, as a centre, firm :
    • 1790, Edmund Burke, Reflections on the Revolution in France, 1803, The Works of The Right Honourable Edmund Burke, Volume 5, page426,
      This was a good, ſtout proof article of faith, pronounced under an anathema, by the venerable fathers of this philoſophick ſynod.
  3. (of alcoholic liquors) Being of a certain standard as to alcohol content.

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proof (third-person singular simple present proofs, present participle proofing, simple past and past participle proofed)

  1. (transitive, intransitive, colloquial) To proofread.
  2. (transitive) To make resistant, especially to water.
  3. (transitive, cooking) To allow to rise (of yeast-containing dough).
  4. (transitive, cooking) To test the activeness of (yeast).

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