prob·​a·​bil·​i·​ty | \ ˌprä-bə-ˈbi-lə-tē \
plural probabilities

Definition of probability

1 : the quality or state of being probable
2 : something (such as an event or circumstance) that is probable
3a(1) : the ratio of the number of outcomes in an exhaustive set of equally likely outcomes that produce a given event to the total number of possible outcomes
(2) : the chance that a given event will occur
b : a branch of mathematics concerned with the study of probabilities
4 : a logical relation between statements such that evidence confirming one confirms the other to some degree

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Synonyms & Antonyms for probability


liability, likelihood


improbability, unlikelihood, unlikeliness

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Examples of probability in a Sentence

There is a low probability that you will be chosen. There is some probability of rain tomorrow. With the dark clouds moving in, rain seems more like a probability than a possibility. The probability of a coin coming up heads is one out of every two tries.
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Recent Examples on the Web

Musk: The only tweets that would have to be, say, reviewed, would be if a tweet had a probability of causing a movement in the stock. Jonathan M. Gitlin, Ars Technica, "Elon Musk on 60 Minutes: “I do not respect the SEC”," 10 Dec. 2018 In aviation systems analysis for certification purposes, a hazardous failure must have a probability of no more than one in 10 million. Dominic Gates, The Seattle Times, "Lion Air pilots struggled against Boeing’s 737 MAX flight-control system, black-box data shows," 27 Nov. 2018 There is pretty clear evidence that democracies with large gaps in income have a much higher probability of breakdown than those with a more egalitarian income distribution. Sean Illing, Vox, "Want less poverty in the world? Empower women.," 5 Nov. 2018 Gregorius’ hit had a hit probability of just 5 percent, the lowest of any base hit on the day and the third lowest of any ball put in play in the game. Eduardo A. Encina,, "Fielding miscues glaring in another ugly Orioles loss, their seventh straight," 2 June 2018 The 90 vertical launch silos, later increased to 96, mean the ship could carry scores of air defense missiles, each of which had a high probability of kill against enemy aircraft, anti-ship missiles, and cruise missiles. Kyle Mizokami, Popular Mechanics, "The USS Fitzgerald Is Built to Take Abuse," 19 June 2017 Reminder: The probability of getting attacked by a shark, at any time, is 1 in 3,748,067. Cady Drell, Marie Claire, "​7 of Your Biggest Shark Week Questions, Answered," 24 July 2018 The approach is model-driven; inVia uses models that consider item popularity and probability of association (putting sunglasses near sunscreen, for example) to adjust warehouse layout automatically and minimize the miles robots must travel. Steven A. Cohen And, WSJ, "Models Will Run the World," 19 Aug. 2018 Anyone searching in Spanish for a match or score will receive highlights, major moments, winning probabilities and lineups. Alyssa Newcomb /, NBC News, "How to watch the 2018 FIFA World Cup if you can't make it to Russia," 14 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'probability.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of probability

15th century, in the meaning defined at sense 1

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Last Updated

8 Jan 2019

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Time Traveler for probability

The first known use of probability was in the 15th century

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More Definitions for probability



English Language Learners Definition of probability

: the chance that something will happen

: something that has a chance of happening

: a measure of how often a particular event will happen if something (such as tossing a coin) is done repeatedly


prob·​a·​bil·​i·​ty | \ ˌprä-bə-ˈbi-lə-tē \
plural probabilities

Kids Definition of probability

1 : the chance of happening The probability of rain is low.
2 : something likely Rain is a probability.
3 : a measure of how likely a given event is The probability of a coin landing face up is ¹/₂.

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Comments on probability

What made you want to look up probability? Please tell us where you read or heard it (including the quote, if possible).


a complex dispute or argument

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