serenade n.

1640s, "a musical performance at night in open air" (especially "one given by a lover under the window of his lady" [OED]), from French sérénade (16c.), from Italian serenata "an evening song," literally "calm sky," from sereno "the open air," noun use of sereno "clear, calm," from Latin serenus "peaceful, calm, serene" (see serene (adj.)). The sense was influenced by Italian sera "evening" (from Latin sera, fem. of serus "late"). The meaning "piece of instrumental music suitable for a serenade" is attested from 1728.

1660s, "perform a serenade," from serenade (n.). Transitive sense, "entertain with nocturnal music," is by 1670s. Related: Serenaded; serenader; serenading.