This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
栨 combines 木 (tree/wood) with 次, but the historical development and original meaning are uncertain.
The kanji visually contains 木 (tree) and 次 (next), but its meaning is unclear. Imagine a rare tree that appears next in a mysterious forest.
For セツ, imagine a set of rare wooden tablets: set -> セツ, and the tree 木 is next 次 in line.