The Collaborative International Dictionary of English v.0.48:

Asphyxiate \As*phyx"i*ate\, v. t.
   To bring to a state of asphyxia; to suffocate.

   Note: [Used commonly in the past pple.]
         [1913 Webster] Asphyxiated

WordNet (r) 3.0 (2006):

asphyxiate
    v 1: deprive of oxygen and prevent from breathing; "Othello
         smothered Desdemona with a pillow"; "The child suffocated
         herself with a plastic bag that the parents had left on the
         floor" [syn: smother, asphyxiate, suffocate]
    2: impair the respiration of or obstruct the air passage of;
       "The foul air was slowly suffocating the children" [syn:
       suffocate, stifle, asphyxiate, choke]
    3: be asphyxiated; die from lack of oxygen; "The child
       suffocated under the pillow" [syn: suffocate, stifle,
       asphyxiate]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "asphyxiate":
   OD, be killed, bottle up, burke, censor, choke, choke off,
   clamp down on, cork, cork up, crack down on, crush, damp down,
   drown, extinguish, famish, gag, garrote, hold down, jump on,
   keep down, keep under, kill, muzzle, pour water on, put down,
   quash, quell, quench, repress, shut down on, silence, sit down on,
   sit on, smash, smother, squash, squelch, stanch, starve, stifle,
   stop the breath, strangle, stultify, subdue, suffocate, suppress,
   throttle