trēˈsȧyȯn noun
( plural tris·agia -yȧ)
Usage: usually capitalized
Etymology: Middle Greek, from neuter of Late Greek trisagios thrice holy, from Greek tris- + hagios holy
1. : a hymn to or invocation of God as the thrice holy
the trisagion of Isa 6:3
2. : a requiem service of the Eastern Church