The Collaborative International Dictionary of English v.0.48:

Gittern \Git"tern\ (g[i^]t"t[~e]rn), n. [OE. giterne, OF.
   guiterne, ultimately from same source as E. guitar. See
   Guitar, and cf. Cittern.]
   An instrument like a guitar. "Harps, lutes, and giternes."
   --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Gittern \Git"tern\, v. i.
   To play on gittern. --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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