This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
櫼 combines 木 (tree/wood) with 韱, which likely contributes a phonetic element. The exact historical development is uncertain, and the character is rare in modern Japanese.
The left side is 木 (tree/wood), and the right side 韱 looks like a dense, intricate structure. Picture a wooden wedge or tool used in carpentry, though the exact meaning is unclear.
For セン, imagine a wooden wedge being sent into a tight gap: send -> セン, and the wood (木) is driven in.