Merriam-Webster Collegiate Dictionary - gastrocnemius

 noun  (plural gastrocnemii)  Etymology: New Latin, from Greek gastrokneme calf of the leg, from gastr- + kneme shank — more at ham  Date: 1676 the largest and most superficial muscle of the calf of the leg arising by two heads from the condyles of the femur and attaching to a tendon that becomes part of the Achilles tendon