/em/ , n. , pl. ems , adj.
n.
1. the letter M, m.
2. Also called mut, mutton . Print.
a. the square of any size of type used as the unit of measurement for matter printed in that type size.
b. (originally) the portion of a line of type occupied by the letter M in type of the same size.
3. See em pica .
adj.
4. Print. having the area of an em quad or the length of an em dash.
[ 1860-65 ]