introitus in·tro·i·tus (ĭn-trō'ĭ-təs)
n. pl. introitus
The entrance into a canal or hollow organ, such as the vagina.
The Kyrie is preceded by the introitus, beginning with a prayer for the departed.
A very old priest, whose features Tristan could not distinguish, began to chant the introitus, in deep long drawn notes.
Francesco stood before the high altar among the monks and acolytes and read the introitus aloud in steady tones.