續一切經音義 2.110

2.110

足跟（下網恩反字統云足後曰跟說文曰足踵也從足根省聲也踵音腫）。

Heels of the feet (足跟: the second character has the fanqie 網 + 恩; Zhitong says, “The back of the foot is called the heel (gēn).” Shuowen says, “The heel (zhǒng) of the foot; it takes 足 with 根 abbreviated for phonetic; zhǒng is pronounced 腫).