The Collaborative International Dictionary of English v.0.48:
Margin \Mar"gin\, n. [OE. margine, margent, L. margo, ginis. Cf.
March a border, Marge.]
1. A border; edge; brink; verge; as, the margin of a river or
2. Specifically: The part of a page at the edge left
uncovered in writing or printing.
3. (Com.) The difference between the cost and the selling
price of an article.
4. Something allowed, or reserved, for that which can not be
foreseen or known with certainty.
5. (Brokerage) Collateral security deposited with a broker to
secure him from loss on contracts entered into by him on
behalf of his principial, as in the speculative buying and
selling of stocks, wheat, etc. It is usually less than the
full value of the security purchased, in which case it may
be qualified by the portion of the full value required to
be deposited; as, to buy stocks on 50% margin. --N.
Margin draft (Masonry), a smooth cut margin on the face of
hammer-dressed ashlar, adjacent to the joints.
Margin of a course (Arch.), that part of a course, as of
slates or shingles, which is not covered by the course
immediately above it. See 2d Gauge.
Syn: Border; brink; verge; brim; rim.