(1):

(n.) A follower of Pelagius, a British monk, born in the later part of the 4th century, who denied the doctrines of hereditary sin, of the connection between sin and death, and of conversion through grace.

(2):

(a.) Of or pertaining to Pelagius, or to his doctrines.

(3):

(a.) Of or pertaining to the sea; marine; pelagic; as, pelagian shells.