introit

noun

Etymology: PIE word *h₁én From Late Middle English introite (“act of entering in or into, entrance; place of entrance”), borrowed from Anglo-Norman introït, introïte (“introit”), or from its etymon Latin introitus (“act of entering in or into, entrance; passage; place of entrance; (figuratively) beginning, introduction, prelude”), from introeō (“to enter, go in”) + -tus (suffix forming action nouns from verbs). Introeō is derived from intrō (“to enter, go into”) (ultimately from Proto-Indo-European *h₁én (“in”)) + eō (“to go”) (ultimately from Proto-Indo-European *h₁ey- (“to go”)).

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.

   “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.]”

2. Any piece of choral music, especially a setting of an anthem or a psalm, sung at the opening of a church service.
3. The action of entering or going in; an entrance.
4. An introduction.