introit

noun4

1. •
   A prayer, typically part of a psalm or other portion of the Bible, read or sung at the start of Mass while or immediately after the priest ascends to the altar.
2. •
   Any piece of choral music, especially a setting of an anthem or a psalm, sung at the opening of a church service.
3. •
   (no longer used) The action of entering or going in; an entrance.
4. •
   (figurative, no longer used) An introduction.