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)]