The Collaborative International Dictionary of English v.0.48:

Expiration \Ex`pi*ra"tion\, n. [L. expiratio,exspiratio: cf. F.
   expiration. See Expire.]
   1. The act of expiring; as:
      (a) (Physiol.) The act or process of breathing out, or
          forcing air from the lungs through the nose or mouth;
          as, respiration consists of inspiration and
          expiration; -- opposed to inspiration.
      (b) Emission of volatile matter; exhalation.
          [1913 Webster]

                The true cause of cold is an expiration from the
                globe of the earth.               --Bacon.
      (c) The last emission of breath; death. "The groan of
          expiration." --Rambler.
      (d) A coming to a close; cessation; extinction;
          termination; end.
          [1913 Webster]

                Before the expiration of thy time. --Shak.
          [1913 Webster]

   2. That which is expired; matter breathed forth; that which
      is produced by breathing out, as a sound.
      [1913 Webster]

            The aspirate "he," which is . . . a gentle
            expiration.                           --G. Sharp.
      [1913 Webster]

WordNet (r) 3.0 (2006):

expiration
    n 1: a coming to an end of a contract period; "the expiry of his
         driver's license" [syn: termination, expiration,
         expiry]
    2: euphemistic expressions for death; "thousands mourned his
       passing" [syn: passing, loss, departure, exit,
       expiration, going, release]
    3: the act of expelling air from the lungs [syn: exhalation,
       expiration, breathing out]