Definition of Irenaeus, St. in US English:
Irenaeus, St.
proper nounˌīrəˈnēəsˌīrəˈnēəs
(c.AD 130–c.200), Greek theologian. He wrote Against Heresies (c.180), a detailed attack on Gnosticism. Feast day (Eastern Church) August 23; (Western Church) June 28.