An Etymological Dictionary of Astronomy and Astrophysics

1. (in humans) The joint between the foot and the leg, in which movement occurs in two planes.
   

   2. The corresponding joint in a quadruped or bird; hock (Dictionary.com).

Etymology (EN): M.E. ankel, enkel, cognate with M.L.G., Du. enkel, O.H.G. anchal, enchil, O.Norse okkul.

Etymology (PE): Quzak, from quz, variant of kuž “humped,” → convex.