Of Celtic origin (see Muireall). Forms of the name are found in Breton as well as in Irish and Scottish Gaelic, and in the form Meriel it was in use in the heart of England in the Middle Ages. The surname Merrill is derived from it. As Muriel it was at first used mainly in Scotland, but became more widely popular during the first half of the 20th century. Since then it has fallen from favour again.