M ( named em ) is the thirteenth  letter of the modern English alphabet and the ISO basic Latin alphabet.
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", . *mā(y)-
Use in writing systems
The letter ⟨m⟩ represents the
bilabial nasal consonant sound [ in the orthography of Latin as well as in that of many modern m] 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]).
Washo, lower-case ⟨m⟩ represents a typical em sound, while upper-case ⟨M⟩ represents a voiceless em sound.
Roman numeral Ⅿ represents the number 1000, though it was not used in Roman times. There is, however, scant evidence that the letter was later introduced in the early centuries by the Romans. 
Unit prefix M (mega), meaning one million times, and m (milli) meaning one-thousandth. m is the standard abbreviation for
metre (or meter) in the International System of Units (SI). However, m is also used as an abbreviation for mile. With money amounts, m means one million: $5m is five million dollars.
M often represents male or masculine, especially in conjunction with F for female or feminine.
M (James Bond) is a fictional character in Ian Fleming's James Bond book and film series In typography, an em dash is a punctuation symbol whose width is equal to that of a capital letter M.
diacritics: Ḿ ḿ Ṁ ṁ Ṃ ṃ M̃ m̃ ᵯ 
IPA-specific symbols related to M: ɱ ɰ Ɱ :
Capital M with hook
Uralic Phonetic Alphabet-specific symbols related to M:
U+1D0D ᴍ LATIN LETTER SMALL CAPITAL M
U+1D1F ᴟ LATIN SMALL LETTER SIDEWAYS TURNED M
U+1D39 ᴹ MODIFIER LETTER CAPITAL M
U+1D50 ᵐ MODIFIER LETTER SMALL M U+1D5A ᵚ MODIFIER LETTER SMALL TURNED M Some symbols related to M were used by the Uralic Phonetic Alphabet prior to its formal standardization in 1902:
U+2098 ₘ LATIN SUBSCRIPT SMALL LETTER M U+A7FA ꟺ LATIN LETTER SMALL CAPITAL TURNED M The
Teuthonista phonetic transcription system uses U+AB3A ꬺ LATIN SMALL LETTER M WITH CROSSED-TAIL  Other variations used for phonetic transcription:
 ᶆ ᶬ ᶭ Ɯ ɯ :
Turned M ꟽ : Inverted M was used in ancient Roman texts to stand for
mulier (woman)  ꟿ : Archaic M was used in ancient Roman texts to abbreviate the personal name 'Manius' (A regular capital M was used for the more common personal name 'Marcus')
 ℳ : currency symbol for Mark
Ancestors and siblings in other alphabets
𐤌 : Semitic letter Mem, from which the following symbols originally derive
Μ μ : Greek letter Mu, from which M derives
Ⲙ ⲙ : Coptic letter Me, which derives from Greek Mu М м :
Cyrillic letter Em, also derived from Mu 𐌌 :
Old Italic M, which derives from Greek Mu, and is the ancestor of modern Latin M
ᛗ : Runic letter Mannaz, which derives from old Italic M 𐌼 : Gothic letter manna, which derives from Greek Mu
Ligatures and abbreviations
LATIN CAPITAL LETTER M
LATIN SMALL LETTER M
Numeric character reference M
EBCDIC family 212
ASCII 1 77
1 Also for encodings based on ASCII, including the DOS, Windows, ISO-8859 and Macintosh families of encodings.
2nd edition (1989); Oxford English Dictionary, (1993); "em," op. cit. Merriam-Webster's Third New International Dictionary of the English Language, Unabridged
^ See F. Simons, "Proto-Sinaitic — Progenitor of the Alphabet"
Rosetta 9 (2011):
Figure Two: "Representative selection of proto-Sinaitic characters with comparison to Egyptian hieroglyphs", (p. 38)
Figure Three: "Chart of all early proto-Canaanite letters with comparison to proto-Sinaitic signs" (p. 39),
Figure Four: "Representative selection of later proto-Canaanite letters with comparison to early proto-Canaanite and proto-Sinaitic signs" (p. 40). See also: Goldwasser (2010), following Albright (1966), "Schematic Table of Proto-Sinaitic Characters" ( fig. 1).
Gordon, Arthur E. (1983). . Illustrated Introduction to Latin Epigraphy University of California Press. p. 45. ISBN 9780520038981 . Retrieved . 3 October 2015
Constable, Peter (2003-09-30). "L2/03-174R2: Proposal to Encode Phonetic Symbols with Middle Tilde in the UCS" (PDF).
Everson, Michael; et al. (2002-03-20). "L2/02-141: Uralic Phonetic Alphabet characters for the UCS" (PDF).
Ruppel, Klaas; Aalto, Tero; Everson, Michael (2009-01-27). "L2/09-028: Proposal to encode additional characters for the Uralic Phonetic Alphabet" (PDF).
Everson, Michael; Dicklberger, Alois; Pentzlin, Karl; Wandl-Vogt, Eveline (2011-06-02). "L2/11-202: Revised proposal to encode "Teuthonista" phonetic characters in the UCS" (PDF).
Constable, Peter (2004-04-19). "L2/04-132 Proposal to add additional phonetic characters to the UCS" (PDF).
^ a b
Perry, David J. (2006-08-01). "L2/06-269: Proposal to Add Additional Ancient Roman Characters to UCS" (PDF).
Media related to M at Wikimedia Commons
The dictionary definition of at Wiktionary M The dictionary definition of at Wiktionary m