This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 腷 is uncertain. It combines the flesh component ⺼ with 畐, but the original semantic and phonetic roles are unclear.
The left side ⺼ suggests flesh or body, and the right side 畐 looks like a container. Picture a body part swelling or being confined, but the exact meaning is uncertain.
For ヒョク, imagine a body part making a soft 'hyok' sound when pressed: hyok -> ヒョク, tied to the flesh component ⺼.