1911 Encyclopædia Britannica/M
M The thirteenth letter of the Phoenician and Greek
alphabets, the twelfth of the Latin, and the thirteenth
of the languages of western Europe. Written originally
from right to left, it took the form 
which survives
in its earliest representations in Greek. The greater length
of the first limb of m is characteristic of the earliest forms. From
this form, written from left to right, the Latin abbreviation M’ for the praenomen Manius is supposed to have developed, the
apostrophe representing the fifth stroke of the original letter.
In the early Greek alphabets the four-stroke M with legs of
equal length represents not m but s; m when written with four
strokes is 
. The five-stroke forms, however, are confined
practically to Crete, Melos and Cumae; from the last named the
Romans received it along with the rest of their alphabet. The
Phoenician name of the symbol was mem, the Greek name μῦ is
formed on the analogy of the name for n. M represents the
bilabial nasal sound, which was generally voiced. It is commonly
a stable sound, but many languages, e.g. Greek, Germanic
and Celtic, change it when final into -n, its dental
correlative. It appears more frequently as an initial sound in
Greek and Latin than in the other languages of the same stock,
because in these s before m (as also before l and n) disappeared at
the beginning of words. The sounds m and b are closely related,
the only difference being that, in pronouncing m, the nasal passage
is not closed, thus allowing the sound to be prolonged,
while b is an instantaneous or explosive sound. In various
languages b is inserted between m and a following consonant,
as in the Gr. μεσημβρία “mid-day,” or the English “number,”
Fr. nombre from Lat. numerus. The sound m can in unaccented
syllables form a syllable by itself without an audible vowel,
e.g. the English word fathom comes from an Anglo-Saxon faþm,
where the m was so used. (For more details as to this phonetic
principle, which has important results in the history of language,
see under N.) (P. Gi.)