Cleanse

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Old English clǣnsian (verb), from clǣne (see clean).

wiktionary

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From Old English clǣnsian, from Proto-West Germanic *klainisōną, from Proto-Germanic *klainiz(“clean”). Cognate with archaic Dutch kleinzen(“to clean; to purify”).

etymonline

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cleanse (v.)

Old English clænsian "to make clean; purge, purify, chasten; justify," from West Germanic *klainson, from *klainoz (see clean (adj.)). Despite its modern spelling (16c.), it retains its Middle English pronunciation. Related: Cleansed; cleansing.