[1] : The Collaborative International Dictionary of English v.0.48

m \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
see also:
em m roof 

[2] : The Collaborative International Dictionary of English v.0.48

em \em\, n. print.
   the portion of a line formerly occupied by the letter m, then
   a square type, used as a unit by which to measure the amount
   of printed matter on a page; the square of the body of a
   type.
   1913 webster

[3] : The Collaborative International Dictionary of English v.0.48

em- \em-\
   a prefix. see en-.
   1913 webster
see also:
en- 

[4] : The Collaborative International Dictionary of English v.0.48

'em \'em\
   an obsolete or colloquial contraction of the old form hem,
   them. --addison.
   1913 webster

[5] : WordNet (r) 2.0

em
     n 1: the square of a body of any size of type syn: mutton, mut
     2: a linear unit 1/6 inch used in printing syn: pica em, pica
see also:
mutton mut pica em pica 

[6] : Virtual Entity of Relevant Acronyms (Version 1.9, June 2002)

em
     extensions manager apple
     
     

[7] : The Free On-line Dictionary of Computing (27 SEP 03)

em
     
        end of medium
     
     
see also:
end of medium 

Em- >> E Words
Em-, definition of term: Em-
em-_pag1.html