"act of causing asphyxia," 1849, noun of action from asphyxiate (v.).
1818, "to suffocate" (someone or something), "produce asphyxia," from asphyxia in its transferred sense + -ate (2). Intransitive sense by 1882. Related: Asphyxiated; asphyxiating.
asphyxiation is sometimes used as a form of torture