introit

noun

1. 1.A composition of vocal music sung at the opening of a church service.
2. 2.An anthem or psalm sung before a Communion service.
3. 3.A part of a psalm or other portion of the Bible read or sung at Mass immediately after the priest ascends to the altar.
4. 4.A psalm sung or chanted immediately before the collect, epistle, and gospel, and while the priest is entering within the rails of the altar, which begins with the line “Requiem aeternam dona eis, Domine” (“Grant them eternal rest, O Lord”).
5. 5.The action of entering or going in; an entrance.