Achilles tendon

Wiktionary

1. n. anatomy The strong tendon formed of the united tendons of the large muscles in the calf of the leg, an inserted into the bone of the heel.

GNU Webster's 1913

1. n. (Anat.) The strong tendon formed of the united tendons of the large muscles in the calf of the leg, an inserted into the bone of the heel; -- so called from the mythological account of Achilles being held by the heel when dipped in the River Styx.

WordNet 3.0

1. n. a large tendon that runs from the heel to the calf