The Collaborative International Dictionary of English v.0.48:

Suffocation \Suf`fo*ca"tion\, n. [L. suffocatio: cf. F.
   suffocation.]
   The act of suffocating, or the state of being suffocated;
   death caused by smothering or choking.
   [1913 Webster]

   Note: The term suffocation is sometimes employed synonymously
         with asphyxia. In the strict medico-legal sense it
         signifies asphyxia induced by obstruction of the
         respiration otherwise than by direct pressure on the
         neck (hanging, strangulation) or submersion (drowning).
         --Quain.
         [1913 Webster]

WordNet (r) 3.0 (2006):

suffocation
    n 1: killing by depriving of oxygen [syn: suffocation,
         asphyxiation]
    2: the condition of being deprived of oxygen (as by having
       breathing stopped); "asphyxiation is sometimes used as a form
       of torture" [syn: suffocation, asphyxiation]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "suffocation":
   abolishment, abolition, annihilation, annulment, asphyxia,
   asphyxiation, burking, choke, choking, choking off, deracination,
   drowning, elimination, eradication, extermination, extinction,
   extinguishment, extirpation, garrote, killing, liquidation,
   liver death, megadeath, negation, nullification, purge,
   rooting out, serum death, silencing, smotheration, smothering,
   snuffing out, starvation, stifling, strangling, strangulation,
   suppression, throttling, uprooting, violent death, voiding,
   watery grave