This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
坺 combines 土 (earth) with 犮, but the exact historical development and original meaning are uncertain.
With 土 (earth) on the left and 犮 on the right, 坺 might suggest something related to soil or ground, but its meaning is unclear.
For ハツ, imagine a hat sitting on a mound of earth: hat -> ハツ, and the earth component 土 ties it to the ground.