Source : Webster's Revised Unabridged Dictionary (1913)

Probability \Prob`a*bil"i*ty\, n.; pl. {Probabilities}. [L.
   probabilitas: cf. F. probabilit['e].]
   1. The quality or state of being probable; appearance of
      reality or truth; reasonable ground of presumption;
      likelihood.

            Probability is the appearance of the agreement or
            disagreement of two ideas, by the intervention of
            proofs whose connection is not constant, but appears
            for the most part to be so.           --Locke.

   2. That which is or appears probable; anything that has the
      appearance of reality or truth.

            The whole life of man is a perpetual comparison of
            evidence and balancing of probabilities.
                                                  --Buckminster.

            We do not call for evidence till antecedent
            probabilities fail.                   --J. H.
                                                  Newman.

   3. (Math.) Likelihood of the occurrence of any event in the
      doctrine of chances, or the ratio of the number of
      favorable chances to the whole number of chances,
      favorable and unfavorable. See 1st {Chance}, n., 5.

   Syn: Likeliness; credibleness; likelihood; chance.

Source : WordNet®

probability
     n 1: a measure of how likely it is that some event will occur;
          "what is the probability of rain?"; "we have a good
          chance of winning" [syn: {chance}]
     2: the quality of being probable [ant: {improbability}]