hygienic (adj.)

1670s, from French hygiène, ultimately from Greek hygieine techne "the healthful art," from hygies "healthy, sound, hearty," literally "living well" (personified as the goddess Hygieia), from PIE *eyu-gwie-es- "having a vigorous life," from root *aiw-, *ayu- "vital force, life, long life, eternity; in the prime of life, young" (source of Latin aevus, English ever). The Greek adjective was used by Aristotle as a noun meaning "health." The difficult spelling in English is a relic of the struggle to render the Greek vowels into French.

1883, from un- (1) "not" + hygienic.