The Collaborative International Dictionary of English v.0.48:

Tamboura \Tam*bour"a\, n.
   1. (Mus.) A stringed musical instrument resembling a lute but
      lacking frets, with a small round body and a long neck,
      used to produce an accompaniment for singing; -- called
      also tambur, tambour, and tampur. [Also spelled
      tambura.]
      [PJC]