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}.