probability

Etymology

From Middle French probabilité, from Latin probābilitās (“probability, credibility”), from probābilis (“probable, credible”).

noun

1. The state of being probable.
   Thus, firſt Traditions were a proof alone; / Cou’d we be certain ſuch they were ſo known: / But ſince ſome Flaws in long deſcent may be, / They make not Truth but Probability. 1682, John Dryden, Religio Laici: Or, A Layman’s Faith, London: H. Hills, published 1710, page 21
   As Demonſtration is the ſhewing the agreement, or diſagreement of two Ideas, by the intervention of one or more Proofs, which have a conſtant, immutable, and viſible connexion one with another : ſo Probability is nothing but the appearance of ſuch an agreement, or diſagreement, by the intervention of Proofs, whoſe connexion is not conſtant and immutable, or at leaſt is not perceived to be ſo, but is, or appears for the moſt part to be ſo, and is enough to induce the Mind to judge the Propoſition to be true, or falſe, rather than the contrary. 1690, John Locke, “Of Probability”, in An Essay Concerning Humane Understanding, 3rd edition, London: Awnsham and John Churchil, published 1695, book IV, page 376
   Thus though this degree of faith is but one remove from disbelief, (denial) nevertheless as much probability is given to one side of the question as the other, and we stand, as it were, on an average between two. 1822, Paul Brown, “Of the Degrees of Faith, according to probability, and force of impression”, in A Disquisition on Faith, Washington, D.C.: […] [F]or the Author[, b]y Andrew Way, page 24
2. An event that is likely to occur.
   These waters wash from the rocks such glistering tinctures, that the ground in some places seemeth as guilded, that better iudgements then ours might haue been perswaded, they contained more then probabilities. 1625, Capt. John Smith, The Trve Travels, Adventvres and Observations, volume I, Richmond: William W. Gray, published 1819, book II, page 115
3. The relative likelihood of an event happening.
   Hoyle said that the probability of life originating on Earth is no greater than the chance that a hurricane, sweeping through a scrapyard, would have the luck to assemble a Boeing 747. 2006, Richard Dawkins, “Why there almost certainly is no God”, in The God Delusion, Boston: Houghton Mifflin, →LCCN, →OL, page 113
4. (mathematics) A number, between 0 and 1, expressing the precise likelihood of an event happening.
   The probability of an event A occurring is denoted P(A).