This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
堛 combines 土 (earth) with 畐, which likely contributes sound. The exact historical development is uncertain.
The left side is earth 土, and the right side 畐 looks like a container or a full vessel. Picture a clod of earth shaped like a small container, but its meaning is unclear.
For ヒョク, imagine a heavy clod of earth making a 'hyock' sound when it hits the ground: hyock -> ヒョク.