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early 15c., from cleanly + -ness.
Cleanliness is indeed next to godliness. [John Wesley, Sermon "On Dress," c.1791]
Old English clænlic "morally pure, innocent," from clæne (see clean (adj.)). Of persons, "habitually clean," from c.1500.
Old English clænlice; see clean (adj.) + -ly (2).