Mu (uppercase Μ, lowercase μ; Ancient Greek  , Modern Greek μι or μυ ) is the 12th letter of the Greek alphabet. In the system of Greek numerals it has a value of 40. Mu was derived from the Egyptian hieroglyphic symbol for water (𓈖), which had been simplified by the Phoenicians and named after their word for water, to become(mem). Letters that arose from mu include the Roman M and the Cyrillic М.