noun

• (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.
• (Christianity, chiefly Protestantism, music) Any piece of vocal music, especially a setting of an anthem or a psalm, sung at the opening of a church service.
• (obsolete) The action of entering or going in; an entrance.
• (obsolete, figuratively) An introduction.