What does Boxing Day have to do with boxing?
late 14c. "moon," also an alchemical name for "silver;" from Latin luna "moon, goddess of the moon," from *leuksna- (cf. Old Church Slavonic luna "moon," Old Prussian lauxnos "stars," Middle Irish luan "light, moon"), from the same source as lux, lumen "light," lucere "to shine" (see light (n.)). The luna moth (1841, American English) so called for the crescent-shaped markings on its wings. Lunarian (1708) was an early word for "inhabitant of the moon."