This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
橖 combines 木 (tree) with 棠, which likely contributes the sound. The exact historical development is uncertain.
The left side is a tree 木, and the right side 棠 looks like a structure with a roof and an opening. Picture a wooden frame used for something, but its exact purpose is unclear.
For トウ, imagine a tall wooden tower: tower -> トウ, and the tree 木 on the left supports the tower-like structure on the right.