osteoma

from WordNet (r) 3.0 (2006)

osteoma
    n 1: a slow growing benign tumor of consisting of bone tissue;
         usually on the skull or mandible

from The Collaborative International Dictionary of English v.0.48

Osteoma \Os`te*o"ma\, n.; pl. {Osteomata}. [NL. See {Osteo-},
   and {-oma}.] (Med.)
   A tumor composed mainly of bone; a tumor of a bone.
   [1913 Webster]