The Collaborative International Dictionary of English v.0.48:

Clarinet \Clar"i*net`\, n. [F. clarinette, dim. of clarine, from
   L. clarus. See Clear, and cf. Clarion.] (Mus.)
   A wind instrument, blown by a single reed, of richer and
   fuller tone than the oboe, which has a double reed. It is the
   leading instrument in a military band.

   Note: [Often improperly called clarionet.]
         [1913 Webster] clarinetist

WordNet (r) 3.0 (2006):

clarinet
    n 1: a single-reed instrument with a straight tube

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "clarinet":
   English horn, Pandean pipe, aulos, basset horn, basset oboe,
   bassoon, block flute, bombard, bourdon, cello, claribel, 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