[ prob-uh-bil-i-tee ]
/ ˌprɒb əˈbɪl ɪ ti /
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noun, plural prob·a·bil·i·ties.

the quality or fact of being probable.
a strong likelihood or chance of something: The probability of the book's success makes us optimistic.
a probable event, circumstance, etc.: Our going to China is a probability.
  1. the relative possibility that an event will occur, as expressed by the ratio of the number of actual occurrences to the total number of possible occurrences.
  2. the relative frequency with which an event occurs or is likely to occur.



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On the farm, the feed for chicks is significantly different from the roosters’; ______ not even comparable.

Idioms for probability

    in all probability, very probably; quite likely: The factory will in all probability be relocated.

Origin of probability

From the Latin word probābilitās, dating back to 1545–55. See probable, -ity
non·prob·a·bil·i·ty, noun, plural non·prob·a·bil·i·ties.su·per·prob·a·bil·i·ty, noun, plural su·per·prob·a·bil·i·ties.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

British Dictionary definitions for probability

/ (ˌprɒbəˈbɪlɪtɪ) /

noun plural -ties

the condition of being probable
an event or other thing that is probable
statistics a measure or estimate of the degree of confidence one may have in the occurrence of an event, measured on a scale from zero (impossibility) to one (certainty). It may be defined as the proportion of favourable outcomes to the total number of possibilities if these are indifferent (mathematical probability), or the proportion observed in a sample (empirical probability), or the limit of this as the sample size tends to infinity (relative frequency), or by more subjective criteria (subjective probability)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for probability

[ prŏb′ə-bĭlĭ-tē ]

A number expressing the likelihood of the occurrence of a given event, especially a fraction expressing how many times the event will happen in a given number of tests or experiments. For example, when rolling a six-sided die, the probability of rolling a particular side is 1 in 6, or 16.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for probability


A number between zero and one that shows how likely a certain event is. Usually, probability is expressed as a ratio: the number of experimental results that would produce the event divided by the number of experimental results considered possible. Thus, the probability of drawing the ten of clubs from an ordinary deck of cards is one in fifty-two (1:52), or one fifty-second.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Idioms and Phrases with probability


see in all probability.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
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