The Collaborative International Dictionary of English v.0.48:

Ossein \Os"se*in\, n. [L. os bone.] (Physiol. Chem.)
   The organic basis of bone tissue; the residue after removal
   of the mineral matters from bone by dilute acid; in embryonic
   tissue, the substance in which the mineral salts are
   deposited to form bone; bone collagen; -- called also
   ostein. Chemically it is the same as collagen.
   [1913 Webster +PJC]