This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
嘳 combines 口 (mouth) with 貴, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side is a mouth 口, and the right side is 貴 (precious). Imagine a precious mouth that sighs or laments, but its exact meaning is unclear.
For カイ, imagine a sighing mouth 口 making a 'kai' sound, like a soft exhalation: kai -> カイ.