This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
櫰 combines 木 (tree) with 褱, which likely contributes the sound. The exact historical development is uncertain.
A tree 木 beside a complex shape 褱. Without a clear meaning, picture a rare, mysterious tree with an unusual name.
For カイ, imagine a rare tree named Kai: Kai -> カイ, and the tree stands alone with its unusual shape.