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.


    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
Related formsnon·prob·a·bil·i·ty, noun, plural non·prob·a·bil·i··per·prob·a·bil·i·ty, noun, plural su·per·prob·a·bil·i·ties. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for probability

Contemporary Examples of probability

Historical Examples of probability

  • Let them ponder on the probability of succeeding with the people.

  • Thus doubtless our hostess reasoned, and in all probability she was right.

    The Roof of France

    Matilda Betham-Edwards

  • Then there was some probability of being put in a coaster; which we might run away with.

    Ned Myers

    James Fenimore Cooper

  • The case is the same with the probability of causes, as with that of chance.

  • So far the probability was against Arthur's being the author.

    The Channings

    Mrs. Henry Wood

British Dictionary definitions for probability


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

Word Origin and History for probability

mid-15c., "quality of being probable," from Old French probabilite (14c.) and directly from Latin probabilitatem (nominative probabilitas) "credibility, probability," from probabilis (see probable). Meaning "something likely to be true" is from 1570s; mathematical sense is from 1718.

Online Etymology Dictionary, © 2010 Douglas Harper

Science definitions for probability



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.

Culture 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.