Pronunciation: (in'trō-it, -troit),[key] —n. 1. Rom. Cath. Ch.a part of a psalm with antiphon recited by the celebrant of the Mass at the foot of the altar and, at High Mass, sung by the choir when the priest begins the Mass.
2. Anglican Ch.,Lutheran Ch.a psalm or anthem sung as the celebrant of the Holy Communion enters the sanctuary.
3. a choral response sung at the beginning of a religious service.