The Collaborative International Dictionary of English v.0.48:

Callosity \Cal*los"i*ty\, n.; pl. Callosities. [L. callasitas;
   cf. F. calost['e].]
   A hard or thickened spot or protuberance; a hardening and
   thickening of the skin or bark of a part, eps. as a result of
   continued pressure or friction.
   [1913 Webster]