 The letter M is derived from the Phoenician Mem, via the Greek Mu (Μ, μ).Semitic Mem is most likely derived from a "Proto-Sinaitic" (Bronze Age) adoption of the "water" ideogram in Egyptian writing.The Egyptian sign had the acrophonic value , from the Egyptian word for "water", "nt"; the adoption as the Semitic letter for was presumably also on acrophonic grounds, from the Semitic word for "water", "*mā(y)-".