1640s, "musical performance at night in open air" (especially one given by a lover under the window of his lady), 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." Sense influenced by Italian sera "evening," from Latin sera, fem. of serus "late." Meaning "piece of music suitable for a serenade" is attested from 1728.
1660s, from serenade (n.). Related: Serenaded; serenading.