Sanctus [Lat., = holy], hymn of the Roman Catholic Mass, beginning, "Holy, holy, holy," from Isa. 6.3; Mat. 21.9. It is the solemn choral ending of the preface. In the old liturgy the second part of the hymn, called Benedictus, was sometimes sung after the elevation. The Sanctus (sometimes called Tersanctus ) also includes the Hosanna.