"clayey soil used for fertilizer," late 14c., from Old French marle (Modern French marne), from Late Latin marglia, diminutive of Latin marga "marl," which is said by Pliny to be a Gaulish word, but modern Celtic cognates are considered to be borrowed from English or French. As a verb by late 14c. Medieval Latin margila is the source of Dutch mergel, German Mergel.