The Collaborative International Dictionary of English v.0.48:

Samisen \Sam"i*sen\, n. [Jap.] (Mus.)
   A Japanese musical instrument with three strings, resembling
   a guitar or banjo.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

samisen
    n 1: a Japanese stringed instrument resembling a banjo with a
         long neck and three strings and a fretted fingerboard and a
         rectangular soundbox; played with a plectrum [syn:
         samisen, shamisen]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "samisen":
   Dobro guitar, F-hole guitar, Spanish guitar, archlute, balalaika,
   banjo, banjo-uke, banjo-ukulele, banjo-zither, banjorine, banjuke,
   bass guitar, centerhole guitar, concert guitar, electric guitar,
   guitar, lute, mando-bass, mando-cello, mandola, mandolin,
   mandolute, mandore, oud, pandora, pandura, sitar, steel guitar,
   tamboura, theorbo, troubadour fiddle, uke, ukulele