1570s, "semi-circular partial horseshoe," from French lunette (13c.), literally "little moon," diminutive of lune "moon," from Latin luna (see luna). Later applied to a wide range of objects and ornamentations resembling more or less a crescent moon.
"hold a second job, especially at night," 1957 (implied in the verbal noun moonlighting), from moonlighter "one who takes a second job after hours" (1954), from the notion of working by the light of the moon; see moonlight (n.). Earlier the verb had been used to mean "commit crimes at night" (1882), from moonlighter in reference to members of organized bands that carried on agrarian outrages in Ireland. And compare moonshine. Moonlighter in American English meant "one of a party who go about serenading on moonlit nights" (by 1897).
moon goddess, equivalent of Latin Luna, from Greek selēnē "the moon; name of the moon goddess," related to selas "light, brightness, bright flame, flash of an eye," from PIE root *swel- (2) "to shine, beam" (source also of Sanskrit svargah "heaven," Lithuanian svilti "to singe," Old English swelan "to be burnt up," Middle Low German swelan "to smolder"); related to swelter, sultry. Related: Selenian "of or pertaining to the moon as a world," 1660s.