Trisagion

from The Collaborative International Dictionary of English v.0.48

Trisagion \Tris*ag"i*on\, n. [NL., fr. Gr. ? thrice holy; ?
   thrice + ? holy.] (Eccl.)
   An ancient anthem, -- usually known by its Latin name
   tersanctus.See {Tersanctus}.
   [1913 Webster]