1530s (n.); 1570s (adj.), from Medieval Latin Pelagianus, from Pelagius, Latinized form of the name of 4c. British monk who denied the doctrine of original sin. Combated by Augustine, condemned by Pope Zosimus in 418 C.E. His name in Welsh was said to have been Morgan, literally "sea-dweller" (hence his Church name, from Greek pelagos "sea;" see pelagic). Related: Pelagianism.