The Collaborative International Dictionary of English v.0.48:

Extinct \Ex*tinct"\, a. [L. extinctus, exstinctus, p. p. of
   extinguere, exstinguere. See Extinguish.]
   1. Extinguished; put out; quenched; as, a fire, a light, or a
      lamp, is extinct; an extinct volcano.
      [1913 Webster]

            Light, the prime work of God, to me is extinct.
                                                  --Milton.
      [1913 Webster]

   2. Without a survivor; without force; dead; as, a family
      becomes extinct; an extinct feud or law.
      [1913 Webster]

   3. Specifically: Once existing as a species but now having no
      living members; -- used of species of living organisms,
      especially of animals and plants; as, dinosaurs are now
      extinct; the dodo bird is extinct.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Extinct \Ex*tinct"\, v. t.
   To cause to be extinct. [Obs.] --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

extinct
    adj 1: no longer in existence; lost or especially having died
           out leaving no living representatives; "an extinct
           species of fish"; "an extinct royal family"; "extinct
           laws and customs" [syn: extinct, nonextant] [ant:
           extant]
    2: (of e.g. volcanos) permanently inactive; "an extinct volcano"
       [ant: active]
    3: being out or having grown cold; "threw his extinct cigarette
       into the stream"; "the fire is out" [syn: extinct,
       out(p)]

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "extinct":
   SOL, ago, all bets off, all gone, all off, all over, all up,
   ancient, annihilated, antediluvian, antiquated, antique, archaic,
   asleep, at an end, away, blown over, by, bygone, bypast, canceled,
   cold, collapsed, complete, concluded, dated, dead, dead and buried,
   deceased, decided, defunct, deleted, demode, departed, disappeared,
   disused, done, done for, done with, dormant, down the drain,
   elapsed, ended, exanimate, expired, expunged, extinguished, fallen,
   fini, finished, forgotten, gone, gone away, gone glimmering,
   gone out, gone-by, had it, has-been, inactive, irrecoverable,
   kaput, kaputt, lapsed, late, lifeless, lost, lost to sight,
   lost to view, missing, no more, nonexistent, obsolete, old hat,
   old-fashioned, out, out of date, out of sight, out of style,
   out of use, outmoded, outworn, over, overthrown, passe, passed,
   passed away, past, past and gone, perfected, perished, quenched,
   run out, set at rest, settled, shot, superseded, terminated,
   through, through with, unanimated, vanished, washed up, wiped out,
   wound up, zapped