The form "Merlin" first appears (as Merlinus) in Geoffrey of Monmouth's History of the Kings of Britain, c. 1136. One suggested reason why Geoffrey didn't latin

The form "Merlin" first appears (as Merlinus) in Geoffrey of Monmouth's History of the Kings of Britain, c. 1136. One suggested reason why Geoffrey didn't latinise the Welsh name more directly as Merdinus is the unfortunate similarity of the latter to the French merde.