introit

1. (Roman Catholicism, music) 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.Examples: "The Glossary of Terms used by ecclesiastics in the middle ages, who describe a day by the “introit,” or commencement of the service appointed by the church to be performed thereon, and an explanation of the Canonical Hours, Watches, &c. will frequently be found useful."; "Adorate Dominum. The introit* and name of the third Sunday after the Epiphany. [Footnote *: Introit.—The first two or more words that form the commencement of a mass, which, from being appropriated to a certain Sunday, or other festival, give the name of such commencement or "introit" to these days.]"; "At some time during these sacerdotal preces the choir will usually have started the sung introit, the exact time for beginning the item dependent on a number of features such as the distance from sacristy to altar."Synonyms: introitus

2. (music, Christianity, chiefly Protestantism) Any piece of choral music, especially a setting of an anthem or a psalm, sung at the opening of a church service.

3. (obsolete) The action of entering or going in; an entrance.

4. (obsolete, figuratively) An introduction.