The Collaborative International Dictionary of English v.0.48:

Bassoon \Bas*soon"\, n. [F. basson, fr. basse bass; or perh. fr.
   bas son low sound. See Bass a part in music. ] (Mus.)
   A wind instrument of the double reed kind, furnished with
   holes, which are stopped by the fingers, and by keys, as in
   flutes. It forms the natural bass to the oboe, clarinet, etc.
   [1913 Webster]

   Note: Its compass comprehends three octaves. For convenience
         of carriage it is divided into two parts; whence it is
         also called a fagot.
         [1913 Webster]

WordNet (r) 3.0 (2006):

bassoon
    n 1: a double-reed instrument; the tenor of the oboe family

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "bassoon":
   English horn, Pandean pipe, aulos, basset horn, basset oboe,
   block flute, bombard, bourdon, cello, claribel, clarinet, clarion,
   concert flute, contrabassoon, contrafagotto, cornet, cornopean,
   cromorna, cromorne, cymbel, diapason, double bassoon, double reed,
   dulciana, fife, fipple flute, flageolet, flute, flute stop,
   foundation stop, fourniture, gamba, gedeckt, gemshorn,
   harmonic flute, hautboy, heckelphone, hornpipe, hybrid stop,
   koppel flute, larigot, licorice stick, melodia, mixture, musette,
   mutation stop, nazard, oaten reed, oboe, oboe da caccia, ocarina,
   octave, organ stop, panpipe, penny-whistle, piccolo, pipe,
   plein jeu, pommer, posaune, principal, quint, quintaten, rank,
   ranket, recorder, reed, reed instrument, reed stop, register,
   rohr flute, sax, saxophone, sesquialtera, shawm, single reed,
   single-reed instrument, sonorophone, spitz flute, stop,
   stopped diapason, stopped flute, string diapason, string stop,
   sweet potato, syrinx, tabor pipe, tenoroon, tierce, tin-whistle,
   tremolo, trombone, trumpet, twelfth, unda maris, vibrato, viola,
   voix celeste, vox angelica, vox humana, whistle, woods, woodwind,
   woodwind choir, woodwind instrument