type of Japanese pagoda tree
槐 refers specifically to a type of Japanese pagoda tree, a deciduous tree known for its compound leaves and fragrant flowers. The meaning is narrow and botanical, without broader abstract extensions.
槐 combines 木 (tree) with 鬼, which likely contributes a phonetic element (カイ) rather than a semantic one. The exact historical development of the compound is uncertain, but the tree radical clearly marks it as a plant name.
A tree (木) with a ghostly (鬼) presence: imagine a pagoda tree whose twisted branches and fragrant blossoms seem almost supernatural, making it the 'ghost tree' 槐.
For カイ, picture a kite (カイト) tangled in the branches of the pagoda tree: kite -> カイ, and the tree catches it like a ghostly hand.