adjective
(church architecture) Of the side of the chancel, apse, altar or choir on which the cantor's (later precentor's) stall is placed (the left hand side to a person facing the altar);
noun
(music) The lower of two choral voice parts sung when a part splits into two; traditionally sung by members of the choir on the cantoris side.
(music) That half of the choir singing cantoris parts, collectively.