The Collaborative International Dictionary of English v.0.48:

Tremolo \Tre"mo*lo\, n. [It. Cf. Tremulous.] (Mus.)
   (a) The rapid reiteration of tones without any apparent
       cessation, so as to produce a tremulous effect.
   (b) A certain contrivance in an organ, which causes the notes
       to sound with rapid pulses or beats, producing a
       tremulous effect; -- called also tremolant, and
       tremulant.
       [1913 Webster]

WordNet (r) 3.0 (2006):

tremolo
    n 1: (music) a tremulous effect produced by rapid repetition of
         a single tone or rapid alternation of two tones
    2: vocal vibrato especially an excessive or poorly controlled
       one

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "tremolo":
   Bebung, English horn, bassoon, block flute, bombard, bourdon,
   cello, claribel, clarinet, clarion, concert flute, cornet,
   cornopean, cromorna, cymbel, diapason, dulciana, falter,
   flute stop, flutter, foundation stop, fourniture, gamba, gedeckt,
   gemshorn, harmonic flute, hybrid stop, koppel flute, larigot,
   melodia, mixture, mutation stop, nazard, oboe, octave, organ stop,
   piccolo, plein jeu, posaune, principal, quaver, quint, quintaten,
   quiver, rank, ranket, reed stop, register, rohr flute,
   sesquialtera, shake, shawm, spitz flute, stop, stopped diapason,
   stopped flute, string diapason, string stop, tierce, tremble,
   tremolando, tremolant, tremor, trill, trillet, trilleto, trillo,
   trombone, trumpet, twelfth, unda maris, vibrato, viola,
   voix celeste, vox angelica, vox humana