The Collaborative International Dictionary of English v.0.48:

Suffocate \Suf"fo*cate\, v. t. [imp. & p. p. Suffocated; p.
   pr. & vb. n. Suffocating.]
   1. To choke or kill by stopping respiration; to stifle; to
      smother.
      [1913 Webster]

            Let not hemp his windpipe suffocate.  --Shak.
      [1913 Webster]

   2. To destroy; to extinguish; as, to suffocate fire.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Suffocating \Suf"fo*ca`ting\,
   a. & n. from Suffocate, v. -- Suf"fo*ca`ting*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

suffocating
    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]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "suffocating":
   airless, breathless, breezeless, censorship, close, crackdown,
   crushing, extinguishment, humid, ill-ventilated, muggy,
   nose-piercing, oppressive, penetrating, pungent, putting down,
   quashing, quelling, quenching, reeking, repression, sharp,
   smashing, smothering, smudgy, squashing, squelching, sticky,
   stifling, strangling, strong, strong-scented, strong-smelling,
   stuffy, subdual, sultry, suppression, throttling, unvented,
   unventilated, windless