The Collaborative International Dictionary of English v.0.48:

Marimba \Ma*rim"ba\, n. [Pg.]
   A musical istrument of percussion, consisting of bars
   yielding musical tones when struck. --Knight.
   [1913 Webster]

WordNet (r) 3.0 (2006):

marimba
    n 1: a percussion instrument with wooden bars tuned to produce a
         chromatic scale and with resonators; played with small
         mallets [syn: marimba, xylophone]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "marimba":
   battery, bells, bones, castanets, celesta, chime, chimes, clappers,
   crash cymbal, cymbals, finger cymbals, gamelan, glockenspiel, gong,
   handbells, idiophone, lyra, maraca, metallophone, orchestral bells,
   percussion, percussion instrument, percussions, percussive, rattle,
   rattlebones, sizzler, snappers, tam-tam, tintinnabula, tonitruone,
   triangle, tubular bells, vibes, vibraphone, xylophone