Trisagion

noun2

1. •
   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.

   • 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. — 1716
2. •
   (Judaism) The kedushah prayer, or Isaiah 6:3 specifically.

   • 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. — 1909