late 14c. "the moon," especially as personified in a Roman goddess answering to Greek Selene; also an alchemical name for "silver;" from Latin luna "moon, goddess of the moon," from PIE *leuksna- (source also of Old Church Slavonic luna "moon," Old Prussian lauxnos "stars," Middle Irish luan "light, moon"), suffixed form of root *leuk- "light, brightness." The luna moth (1841, American English) so called for the crescent-shaped eye-spots on its wings.