This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
躻 combines 身 (body) and 空 (empty). The exact historical development is uncertain, but it likely expresses a concept of bodily emptiness or foolishness.
An empty body: 身 (body) + 空 (empty) suggests a person who is vacant or foolish.
For うつけ, imagine an empty-headed person saying 'utsuke' as a silly sound: the hollow body 躻 utters 'utsuke'.
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