This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蟤 combines 虫 (insect) with 巽, which likely contributes the sound. The exact historical development is uncertain.
The insect radical 虫 suggests a bug-related meaning, but the overall idea is obscure. Picture a mysterious insect whose name is lost to time.
For セン, imagine a centipede (a many-legged insect) crawling beside the 巽 component: cent -> セン, tying the insect radical to the reading.
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