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.
      [1913 Webster]

            I took my leave, being half stifled with the
            closeness of the room.                --Swift.
      [1913 Webster]

   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.
      [1913 Webster]

   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]

The Collaborative International Dictionary of English v.0.48:

Stifled \Sti"fled\, a.
   Stifling.
   [1913 Webster]

         The close and stifled study.             --Hawthorne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stifled
    adj 1: held in check with difficulty; "a smothered cough"; "a
           stifled yawn"; "a strangled scream"; "suppressed
           laughter" [syn: smothered, stifled, strangled,
           suppressed]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "stifled":
   arcane, bated, blurred, breathy, cabalistic, censored, choked,
   choking, classified, close, closed, concealed, croaking, crushed,
   cryptic, damped, dampened, dark, dead, deadened, drawling, drawly,
   dull, dulled, dysphonic, enigmatic, esoteric, flat, guttural,
   harsh, hawking, hermetic, hidden, hoarse, hush-hush, inarticulate,
   indistinct, latent, lisping, mispronounced, muffled, muted, muzzy,
   mysterious, nasal, occult, quashed, quavering, quelled, repressed,
   restricted, secret, shaking, shaky, smashed, smothered, snuffling,
   softened, sordo, squashed, squelched, strangled, subdued,
   suffocated, suppressed, thick, throaty, top secret, tremulous,
   twangy, ulterior, unbreatheable, under security, under wraps,
   undisclosable, undisclosed, undivulgable, undivulged, unrevealable,
   unrevealed, unspoken, untellable, untold, unutterable, unuttered,
   unwhisperable, velar