This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
哾 combines 口 (mouth) with 兌, which likely contributes a phonetic element. The exact historical development is uncertain.
With 口 (mouth) on the left and 兌 on the right, 哾 might suggest something related to speech or sound, but its meaning is unclear.
For セツ, imagine a set of lips (口) making a sound: set -> セツ, though the exact meaning is uncertain.