The Collaborative International Dictionary of English v.0.48:

Violin \Vi`o*lin"\, n. [It. violino, dim. of viola. See Viol.]
   (Mus.)
   A small instrument with four strings, played with a bow; a
   fiddle.
   [1913 Webster]

   Note: The violin is distinguished for the brilliancy and
         gayety, as well as the power and variety, of its tones,
         and in the orchestra it is the leading and most
         important instrument.
         [1913 Webster]

WordNet (r) 3.0 (2006):

violin
    n 1: bowed stringed instrument that is the highest member of the
         violin family; this instrument has four strings and a
         hollow body and an unfretted fingerboard and is played with
         a bow [syn: violin, fiddle]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "violin":
   A string, Amati, Cremona, D string, E string, G string, Strad,
   Stradivari, Stradivarius, bass, bass viol, bow, bridge,
   bull fiddle, cello, contrabass, crowd, double bass, fiddle,
   fiddlebow, fiddlestick, fingerboard, kit, kit fiddle, kit violin,
   scroll, soundboard, string, tenor violin, tuning peg, viola,
   violinette, violoncello, violoncello piccolo, violone, violotta