Source : Webster's Revised Unabridged Dictionary (1913)

Osteoclast \Os"te*o*clast\, n. [Osteo- + Gr. ? to break.]
   1. (Physiol.) A myeloplax.

   Note: The osteoclasts occur usually in pits or cavities which
         they appear to have excavated, and are supposed to be
         concerned in the absorption of the bone matrix.

   2. An instrument for performing osteoclasis.

Source : WordNet®

osteoclast
     n : cell that functions in the breakdown and resorption of bone
         tissue