tris·agion \trēˈsȧyȯn\noun (pluraltris·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