The Collaborative International Dictionary of English v.0.48:

Asphyxiation \As*phyx`i*a"tion\, n.
   The act of causing asphyxia; a state of asphyxia.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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