This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 櫐 is uncertain. It visually combines 畾 (a triple-field shape) with 木 (tree/wood), but the original semantic and phonetic roles are unclear.
With no clear meaning, picture a dense thicket of trees (木) growing over layered fields (畾) — a tangled, obscure scene that mirrors the kanji's obscurity.
For ルイ, imagine a vine (ふじ, a kun reading) wrapping around the layered fields and tree, and a voice saying 'rui' as it tangles: rui -> ルイ.