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 mediæval churc...