The Collaborative International Dictionary of English v.0.48:

Tinnitus \Tin*ni"tus\, n. [L., fr. tinnire to jingle.] (Med.)
   A ringing, whistling, or other imaginary noise perceived in
   the ears; -- called also tinnitus aurium.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tinnitus
    n 1: a ringing or booming sensation in one or both ears; a
         symptom of an ear infection or Meniere's disease