the strong tendon joining the muscles in the calf of the leg to the bone of the heel -- called also tendon of Achilles.
Achilles, Greek mythological character. One of the most illustrious of warriors, Achilles was the offspring of a sea nymph who sought to achieve immortality for her son by dipping him in the river Styx in Hades. Holding Achilles by the heel, she left this one area unprotected. Later, in the Trojan War, he was fatally wounded when an arrow struck the very spot where he was vulnerable. Since classical times, the heel and Achilles have been commonly associated.
by Merriam-Webster Inc.