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M (named em /ˈɛm/) is the thirteenth letter of the modern English alphabet and the ISO basic Latin alphabet.

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 /n/, from the Egyptian word for "water", nt; the adoption as the Semitic letter for /m/ was presumably also on acrophonic grounds, from the Semitic word for "water", .

The letter ⟨m⟩ represents the bilabial nasal consonant sound [m] in the orthography of Latin as well as in that of many modern languages, and also in the International Phonetic Alphabet. In English, the Oxford English Dictionary (first edition) says that ⟨m⟩ is sometimes a vowel in words like spasm and in the suffix -ism. In modern terminology, this is described as a syllabic consonant (IPA [m̩]).

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