The Collaborative International Dictionary of English v.0.48:

Absurdity \Ab*surd"i*ty\ (-[i^]*t[y^]), n.; pl. Absurdities
   (-t[i^]z). [L. absurditas: cf. F. absurdite.]
   1. The quality of being absurd or inconsistent with obvious
      truth, reason, or sound judgment. "The absurdity of the
      actual idea of an infinite number." --Locke.
      [1913 Webster]

   2. That which is absurd; an absurd action; a logical
      contradiction.
      [1913 Webster]

            His travels were full of absurdities. --Johnson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

absurdity
    n 1: a message whose content is at variance with reason [syn:
         absurdity, absurdness, ridiculousness]
    2: a ludicrous folly; "the crowd laughed at the absurdity of the
       clown's behavior" [syn: absurdity, fatuity,
       fatuousness, silliness]

The Devil's Dictionary (1881-1906):

ABSURDITY, n.  A statement or belief manifestly inconsistent with
one's own opinion.