Source : Webster's Revised Unabridged Dictionary (1913)

Eburnation \E`bur*na"tion\, n. [L. eburnus of ivory, fr. ebur
   ivory: cf. F. ['e]burnation. See {Ivory}.] (Med.)
   A condition of bone cartilage occurring in certain diseases
   of these tissues, in which they acquire an unnatural density,
   and come to resemble ivory.

Source : WordNet®

eburnation
     n : a change that occurs in degenerative joint disease in which
         bone is converted into a dense smooth substance
         resembling ivory