The Collaborative International Dictionary of English v.0.48:
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. [1913 Webster]WordNet (r) 3.0 (2006):
masseter n 1: a large muscle that raises the lower jaw and is used in chewing