suffocative

from WordNet (r) 3.0 (2006)

suffocative
    adj 1: causing difficulty in breathing especially through lack
           of fresh air and presence of heat; "the choking June
           dust"; "the smothering soft voices"; "smothering heat";
           "the room was suffocating--hot and airless" [syn:
           {smothering}, {suffocating}, {suffocative}]

from The Collaborative International Dictionary of English v.0.48

Suffocative \Suf"fo*ca*tive\, a.
   Tending or able to choke or stifle. "Suffocative catarrhs."
   --Arbuthnot.
   [1913 Webster]