This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
樝 combines 木 (tree) with 虘, which likely contributes sound. The exact historical development is uncertain.
The left side 木 suggests a tree or wood, but the overall meaning is unclear. Picture an unknown tree with a strange name.
For サ, imagine a sapling (サ) of this mysterious tree: sapling -> サ, tied to the 木 component.