The Collaborative International Dictionary of English v.0.48:

orgasm \or"gasm\ ([^o]r"g[a^]z'm), n. [F. orgasme; cf. Gr.
   'orgasmo`s a kneading, softening, prob. confused with 'orga^n
   to swell, especially with lust; to feel an ardent desire.]
   (Physiol.)
   Eager or immoderate excitement or action; the state of
   turgescence of any organ; erethism.
   [1913 Webster]

   2. Especially: The peak of the physical pleasurable sexual
      excitement caused by stimulation of the sexual organs, as
      in intercourse; in the male, it is usually accompanied by
      ejaculation.
      [1913 Webster +PJC]

   3. Hence: An eruption of intense, uncontrolled excitement; --
      used of groups and individuals.
      [PJC]

WordNet (r) 3.0 (2006):

orgasm
    n 1: the moment of most intense pleasure in sexual intercourse
         [syn: orgasm, climax, sexual climax, coming]