The Collaborative International Dictionary of English v.0.48:

Exostosis \Ex`os*to"sis\, n. [NL., fr. Gr. ?; ? out + ? bone:
   cf. F ? exostose.]
   1. (Med.) Any protuberance of a bone which is not natural; an
      excrescence or morbid enlargement of a bone. --Coxe.
      [1913 Webster]

   2. (Bot.) A knot formed upon or in the wood of trees by
      disease. Exoteric

WordNet (r) 3.0 (2006):

exostosis
    n 1: a benign outgrowth from a bone (usually covered with
         cartilage)