This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
咑 combines 口 (mouth) with 打 (strike). The exact historical development is uncertain, and it may be a variant or a character used primarily for its sound value.
A mouth 口 beside a striking hand 打 suggests a sound made by hitting, but the meaning is unclear.
For ダ, imagine the sound of a dull thud: da! The mouth 口 and striking hand 打 together make a da sound.
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