Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

Source : WordNet®

exostosis
     n : a benign outgrowth from a bone (usually covered with
         cartilage)
     [also: {exostoses} (pl)]