Source : Webster's Revised Unabridged Dictionary (1913)

Sanctus \Sanc"tus\, n. [L. sanctus, p. p. of sancire.]
   1. (Eccl.) A part of the Mass, or, in Protestant churches, a
      part of the communion service, of which the first words in
      Latin are Sanctus, sanctus, sanctus [Holy, holy, holy]; --
      called also {Tersanctus}.

   2. (Mus.) An anthem composed for these words.

   {Sanctus bell}, a small bell usually suspended in a bell cot
      at the apex of the nave roof, over the chancel arch, in
      medi[ae]val churches, but a hand bell is now often used;
      -- so called because rung at the singing of the sanctus,
      at the conclusion of the ordinary of the Mass, and again
      at the elevation of the host. Called also {Mass bell},
      {sacring bell}, {saints' bell}, {sance-bell}, {sancte
      bell}.

Tersanctus \Ter*sanc"tus\, n. [L. ter thrice + sanctus holy.]
   (Eccl.)
   An ancient ascription of praise (containing the word ``Holy''
   -- in its Latin form, ``Sanctus'' -- thrice repeated), used
   in the Mass of the Roman Catholic Church and before the
   prayer of consecration in the communion service of the Church
   of England and the Protestant Episcopal Church. Cf.
   {Trisagion}.