late 14c., "the evening star," from Old French vespre, from Latin vesper (masc.), vespera (fem.) "evening star, evening, west," related to Greek hesperos, and ultimately from PIE *wespero- (cf. Old Church Slavonic večeru, Lithuanian vakaras, Welsh ucher, Old Irish fescor "evening"), from root *we- "down" (cf. Sanskrit avah "down, downward"). Meaning "evening" is attested from c.1600.
Vespers "sixth canonical hour" is attested from 1610s, from plural of Latin vespera "evening;" the native name was evensong (Old English æfen-sang).
evening prayer of thanksgiving and praise in Roman Catholic and certain other Christian liturgy. Vespers and lauds (morning prayer) are the oldest and most important of the traditional liturgy of the hours. Many scholars believe vespers is based on Judaic forms of prayer and point to a daily evening celebration observed among Jews in the first century before Christ.