noun
introit
A Christian liturgical term referring to the entrance chant or antiphon sung at the beginning of Mass.
ミサの初めに聖歌隊が入祭唱を歌った。
The choir sang the introit at the beginning of Mass.
Compound of 入 (entering), 祭 (festival/ritual, here referring to Mass), and 唱 (chant). The term is a direct translation of the Latin 'introitus'.