The Collaborative International Dictionary of English v.0.48:

Mandolin \Man"do*lin\, Mandoline \Man"do*line\, n. [F.
   mandoline, It. mandolino, dim. of mandola, fr. L. pandura.
   See Bandore.] (Mus.)
   A small and beautifully shaped instrument resembling the
   lute.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mandolin
    n 1: a stringed instrument related to the lute, usually played
         with a plectrum

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "mandolin":
   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, mandolute, mandore,
   oud, pandora, pandura, samisen, sitar, steel guitar, tamboura,
   theorbo, troubadour fiddle, uke, ukulele