The Collaborative International Dictionary of English v.0.48:

Stifle \Sti"fle\, v. t. [imp. & p. p. Stifled; p. pr. & vb. n.
   Stifling.] [Freq. of OE. stif stiff; cf. Icel. st[imac]fla
   to dam up.]
   1. To stop the breath of by crowding something into the
      windpipe, or introducing an irrespirable substance into
      the lungs; to choke; to suffocate; to cause the death of
      by such means; as, to stifle one with smoke or dust.
      [1913 Webster]

            Stifled with kisses, a sweet death he dies.
                                                  --Dryden.
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            I took my leave, being half stifled with the
            closeness of the room.                --Swift.
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   2. To stop; to extinguish; to deaden; to quench; as, to
      stifle the breath; to stifle a fire or flame.
      [1913 Webster]

            Bodies . . . stifle in themselves the rays which
            they do not reflect or transmit.      --Sir I.
                                                  Newton.
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   3. To suppress the manifestation or report of; to smother; to
      conceal from public knowledge; as, to stifle a story; to
      stifle passion.
      [1913 Webster]

            I desire only to have things fairly represented as
            they really are; no evidence smothered or stifled.
                                                  --Waterland.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stifling
    adj 1: characterized by oppressive heat and humidity; "the
           summer was sultry and oppressive"; "the stifling
           atmosphere"; "the sulfurous atmosphere preceding a
           thunderstorm" [syn: sultry, stifling, sulfurous,
           sulphurous]
    n 1: forceful prevention; putting down by power or authority;
         "the suppression of heresy"; "the quelling of the
         rebellion"; "the stifling of all dissent" [syn:
         suppression, crushing, quelling, stifling]