Source : Webster's Revised Unabridged Dictionary (1913)

Masseter \Mas"se*ter\, n. [NL., fr. Gr. ? a chewer, ? a muscle
   of the lower jaw used in chewing, from ? to chew: cf. F.
   mass['e]ter.] (Anat.)
   The large muscle which raises the under jaw, and assists in
   mastication.

Source : WordNet®

masseter
     n : a large muscle that raises the lower jaw and is used in
         chewing