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]

Moby Thesaurus II by Grady Ward, 1.0:

151 Moby Thesaurus words for "expiration":
   Aqua-Lung, Z, annihilation, apodosis, artificial respiration,
   aspiration, asthmatic wheeze, bane, biological death, breath,
   breath of air, breathing, broken wind, catastrophe, ceasing,
   cessation, cessation of life, clinical death, close, closing, coda,
   concluding, conclusion, consummation, cough, crack of doom,
   crossing the bar, culmination, curtain, curtains, death,
   death knell, debt of nature, decease, demise, denouement,
   departure, destination, destiny, discontinuance, discontinuation,
   dissolution, doom, dying, ebb of life, effect, end, end of life,
   end point, ending, envoi, epilogue, eschatology, eternal rest,
   exhalation, exit, expiry, exsufflation, extinction, extinguishment,
   fate, final solution, final summons, final twitch, final words,
   finale, finality, finger of death, finis, finish, gasp, goal,
   going, going off, grave, gulp, hack, hand of death, hiccup,
   inhalation, inhalator, inspiration, insufflation, iron lung,
   izzard, jaws of death, knell, last, last breath, last debt,
   last gasp, last muster, last rest, last roundup, last sleep,
   last things, last trumpet, last words, latter end, leaving life,
   loss of life, making an end, mouth-to-mouth resuscitation, omega,
   oxygen mask, oxygen tent, pant, parting, passing, passing away,
   passing over, payoff, period, perishing, peroration, puff, quietus,
   release, resolution, respiration, rest, resting place, reward,
   scuba, sentence of death, shades of death, shadow of death, sigh,
   sleep, sneeze, sniff, sniffle, snore, snoring, snuff, snuffle,
   somatic death, sternutation, stertor, stoppage, stopping place,
   summons of death, suspiration, swan song, term, terminal,
   termination, terminus, wheeze, wind, windup



Bouvier's Law Dictionary, Revised 6th Ed (1856):

EXPIRATION. Cessation; end. As, the expiration of, a lease, of a contract,
or statute.
     2. In general, the expiration of a contract puts an end to all the
engagements of the parties, except to those which arise from the non-
fulfillment of obligations created during its existence. For example, the
expiration of a partnership so dissolves it, that the parties cannot in
general create any new liability, but it still subsists, to enable the
parties to fulfill engagements in which the partners have engaged, or to
compel others to perform their obligations towards them. See Dissolution;
Contracts.
     3. When a statute is limited as to time, it expires by mere lapse of
time, and then it has no force whatever; and, if such a statute repealed or
supplied a former statute, the first statute is, i so facto, revived by the
expiration of the repealing statute; 6 Whart. 294; 1 Bland, R. 664 unless it
appear that such was not the intention of the legislature. 3 East, 212 Bac.
Ab. Statute, D.