Trisagion

From Medieval Latin trisagion, from Byzantine Greek τρισάγιον (triságion), from τρίς (trís, “thrice”) + ἅγιον (hágion, “holy”).

Trisagion (plural Trisagia or Trisagions)

1. (Christianity) A liturgical prayer that runs “Holy God, Holy Mighty, Holy Immortal, have mercy on us” in English, typically sung before certain scriptural readings at Eucharistic liturgies in Eastern Christianity, and during the Good Friday service in the Roman Rite.
   • 1716, Thomas Browne, edited by Samuel Johnson, Christian Morals‎^[1], 2nd edition, London: J. Payne, published 1756, Part I, p. 24:

     With these sure graces, while busy tongues are crying out for a drop of cold water, mutes may be in happiness, and sing the Trisagion in heaven.

2. (Judaism) The kedushah prayer, or Isaiah 6:3 specifically.
   • 1909, David de Sola Pool, “Appendix A”, in The Kaddish: Inaugural Dissertation‎^[2], W. Drugulin in Leipzig, pages 100–101:

     The holy praise, the prayer dealing with holiness par excellence, would be an inept designation in view of the use of the Trisagion in the liturgy.

• Tersanctus

• rigatonis