The Collaborative International Dictionary of English v.0.48:

Embouchure \Em`bou`chure"\, n. [F., fr. emboucher to put to the
   mouth; pref. em- (L. in) + bouche the mouth. Cf. Embouge,
   Debouch.]
   1. The mouth of a river; also, the mouth of a cannon.
      [1913 Webster]

   2. (Mus.)
      (a) The mouthpiece of a wind instrument.
      (b) The shaping of the lips to the mouthpiece; as, a flute
          player has a good embouchure.
          [1913 Webster]

WordNet (r) 3.0 (2006):

embouchure
    n 1: the aperture of a wind instrument into which the player
         blows directly [syn: mouthpiece, embouchure]