M's the thirteenth letter of the modern Latin alphabet. Its name in English 's spelled em. History The letter M derives its shape from the Phoenician Mem, via the Greek Mu (Μ, μ). Semitic Mem probably originally pictured water. It's known that Semitic people working in Egypt c. 2000 BC borrowed a hieroglyph for Water that was first used for an alveolar nasal (/n/, because of the Egyptian word for Water, "n-t". This same symbol became used for M in Semitic, because their word for water… (More on M)