Source : Webster's Revised Unabridged Dictionary (1913)

Gastrocnemius \Gas`troc*ne"mi*us\, n. [NL., from Gr. ? the calf
   of the leg.] (Anat.)
   The muscle which makes the greater part of the calf of the
   leg.

Source : WordNet®

gastrocnemius
     n : the muscle in the back part of the leg that forms the
         greater part of the calf; responsible for the plantar
         flexion of the foot [syn: {gastrocnemius muscle}]