The Collaborative International Dictionary of English v.0.48:

Cittern \Cit"tern\, n. [L.cithara, Gr. kiqa`ra. Cf. Cithara,
   Gittern.] (Mus.)
   An instrument shaped like a lute, but strung with wire and
   played with a quill or plectrum. [Written also cithern.]
   --Shak.
   [1913 Webster]

   Note: Not to be confounded with zither.
         [1913 Webster]

WordNet (r) 3.0 (2006):

cittern
    n 1: a 16th century musical instrument resembling a guitar with
         a pear-shaped soundbox and wire strings [syn: cittern,
         cithern, cither, citole, gittern]