This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
榍 combines 木 (tree/wood) with 屑, which likely contributes the sound. The exact historical development is uncertain.
The tree 木 beside 屑 suggests wood fragments or scraps, but the kanji's meaning is uncertain.
For セツ, imagine a set of wooden scraps: set -> セツ, and the tree 木 provides the wood.
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