nocturn (n.)

also nocturne, name of a division of the office of matins said just before daybreak (in the early Church a service recited after midnight), c. 1200, from Old French nocturne "evening service; curfew," from Medieval Latin nocturna, "group of Psalms used in the nocturns," from Latin nocturnus "pertaining or belonging to the night" (see nocturnal).