The same as champaign, a flat, open country; from Champ, an open, level field or plain, and lean, a meadow; laine, Gaelic, full; leathann, wide; Cor. Br., laun; Welsh, llann, full, wide.
Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.