The term is from Latin meaning "place of the cantor." Traditionally, the cantor sat on the north side of the cathedral. In antiphonal singing, the term cantoris indicates those who sit on the cantoral or cantor's side of the choir of a church or cathedral. The opposite side is known as "decani." The terms were used in The Hymnal (1940) version of "Ye watchers and ye holy ones" to designate different parts for singing the antiphonal alleluias.
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from "An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians," Don S. Armentrout and Robert Boak Slocum, editors.