M (&ebreve_;m). 1. M, the thirteenth letter of the English alphabet, is a vocal consonant, and from the manner of its formation, is called the labio-nasal consonant. See Guide to Pronunciation, §§ 178-180, 242.[1913 Webster]
The letter M came into English from the Greek, through the Latin, the form of the Greek letter being further derived from the Phœnician, and ultimately, it is believed, from the Egyptian. Etymologically M is related to n, in lime, linden; emmet, ant; also to b.[1913 Webster] M is readily followed by b and p. the position of the lips in the formation of both letters being the same. The relation of b and m is the same as that of d and t to n. and that of g and k to ng.[1913 Webster]
2. As a numeral, M stands for one thousand, both in English and Latin.[1913 Webster]
M, n. 1. (Print.) A quadrat, the face or top of which is a perfect square; also, the size of such a square in any given size of type, used as the unit of measurement for that type: 500 m's of pica would be a piece of matter whose length and breadth in pica m's multiplied together produce that number. [Written also em.][1913 Webster]
2. (law) A brand or stigma, having the shape of an M, formerly impressed on one convicted of manslaughter and admitted to the benefit of clergy.[1913 Webster]
M roof (Arch.), a kind of roof formed by the junction of two common roofs with a valley between them, so that the section resembles the letter M.[1913 Webster]