The Columbia Encyclopedia, Sixth Edition. 2001-07.
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.