gas·troc·ne·mi·us 
(găs′trŏk-nēmē-əs, găs′trə-)
(găs′trŏk-nēmē-əs, găs′trə-)n. pl. gas·troc·ne·mi·i (-mē-ī′)
The largest, most prominent muscle of the calf of the leg, the action of which extends the foot and bends the knee.
[New Latin gastrocnēmius, from Greek gastroknēmiā, calf of the leg : gastro-, belly (from its bellylike shape); see GASTRO- + knēmē, leg.]