The Collaborative International Dictionary of English v.0.48:

Improbability \Im*prob`a*bil"i*ty\, n.; pl. Improbabilities.
   [Cf. F. improbabilit['e].]
   The quality or state of being improbable; unlikelihood; also,
   that which is improbable; an improbable event or result.
   [1913 Webster]