Achilles tendon

tendon which attaches the heel bone of the foot to the calf muscle (Anatomy)

This is about vertebrate anatomy. For the metaphor of a single vulnerable spot, see Achilles' heel. The Achilles tendon (or occasionally Achilles’ tendon) also known as the calcaneal tendon or the tendocalcaneous is a tendon of the posterior leg. It serves to attach the gastrocnemius (calf) and soleus muscles to the calcaneus (heel) bone.
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Achilles tendon n. The large tendon connecting the heel bone to the calf muscle of the leg. Also called calcanean tendon, heel tendon. [more]Achilles tendon - Community and Resources

Noun
1. a large tendon that runs from the heel to the calf
(synonym) tendon of Achilles
(hypernym) tendon, sinew
(part-holonym) calf, sura

noun
tendon at the back of the ankle which connects the calf muscles to the heel and which acts to pull up the heel when the calf muscle is contracted