This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
墲 combines 土 (earth) with 無, which likely contributes sound. The exact historical development is uncertain.
The left side is earth 土, and the right side is 無, which can suggest nothingness. Picture a patch of earth where nothing grows, leaving its meaning uncertain.
For ボ, imagine a barren patch of earth with a single bone resting on it: bone -> ボ, and the earth holds nothing else.
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