Source : Webster's Revised Unabridged Dictionary (1913)

Guitar \Gui*tar"\, n. [F. guitare; cf. Pr., Sp., & Pg. guitarra,
   It. chitarra; all fr. Gr. ?; cf. L. cithara. Cf. {Cittern},
   {Gittern}.]
   A stringed instrument of music resembling the lute or the
   violin, but larger, and having six strings, three of silk
   covered with silver wire, and three of catgut, -- played upon
   with the fingers.

Source : WordNet®

guitar
     n : a stringed instrument usually having six strings; played by
         strumming or plucking