The Collaborative International Dictionary of English v.0.48:

Margin \Mar"gin\, v. t. [imp. & p. p. Margined; p. pr. & vb.
   n. Marginging.]
   1. To furnish with a margin.
      [1913 Webster]

   2. To enter in the margin of a page.
      [1913 Webster]

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
      lake.
      [1913 Webster]

   2. Specifically: The part of a page at the edge left
      uncovered in writing or printing.
      [1913 Webster]

   3. (Com.) The difference between the cost and the selling
      price of an article.
      [1913 Webster]

   4. Something allowed, or reserved, for that which can not be
      foreseen or known with certainty.
      [1913 Webster]

   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.
      Biddle.
      [1913 Webster]

   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.
      [1913 Webster]

   Syn: Border; brink; verge; brim; rim.
        [1913 Webster]

WordNet (r) 3.0 (2006):

margin
    n 1: the boundary line or the area immediately inside the
         boundary [syn: margin, border, perimeter]
    2: an amount beyond the minimum necessary; "the margin of
       victory"
    3: the amount of collateral a customer deposits with a broker
       when borrowing from the broker to buy securities [syn:
       margin, security deposit]
    4: (finance) the net sales minus the cost of goods and services
       sold [syn: gross profit, gross profit margin, margin]
    5: the blank space that surrounds the text on a page; "he jotted
       a note in the margin"
    6: a permissible difference; allowing some freedom to move
       within limits [syn: allowance, leeway, margin,
       tolerance]

Moby Thesaurus II by Grady Ward, 1.0:

188 Moby Thesaurus words for "margin":
   abut, adjoin, aesthetic distance, air space, allowance,
   ample scope, balance, bank, befringe, bind, blank check, board,
   bonus, border, bordure, bound, boundary line, bounds, brim, brink,
   brow, caesura, carte blanche, caution, caution money, clearance,
   coast, collateral, collateral security, compass, connect,
   deep space, delicacy, delicate distinction, deposit,
   depths of space, differentia, differential, discontinuity,
   distance, distance between, distinction, divergence, dividend,
   double space, edge, elbowroom, em space, en space, enframe,
   exhaust price, extent, extra, farness, featheredge, field,
   fine point, flange, forfeit, frame, free course, free hand,
   free play, free scope, freeboard, freedom, fringe, frontier,
   full scope, full swing, gratuity, hair space, hairline, half space,
   headroom, hem, hiatus, infinity, interim, intermediate space,
   interruption, interspace, interstice, interval, join, jump,
   labellum, labium, labrum, lacuna, lagniappe, lap, latitude, leap,
   ledge, leeway, leftover, length, light-years, limb, limbus, limits,
   line, lip, list, long rope, maneuvering space, march, marge,
   marginate, mileage, minimum, narrow margin, neighbor,
   nice distinction, nicety, no holds barred, nuance, open space,
   outline, overage, overmeasure, overplus, overrun, overset,
   overstock, oversupply, parsecs, particle of difference, perimeter,
   periphery, perspective, piece, play, plus, point of difference,
   pourboire, purfle, purl, ragged edge, range, reach, refinement,
   remainder, remoteness, rim, room, room to spare, rope, scope,
   sea room, selvage, separation, set off, shade of difference,
   shoestring margin, shore, side, sideline, single space, skirt,
   something extra, space, space between, span, spare, spare room,
   stake, stretch, stride, subtle distinction, subtlety, surplus,
   surplusage, surround, swing, thin margin, time interval, tip,
   tolerance, touch, trim, trimming, verge, way, ways, wide berth,
   wide margin