The Collaborative International Dictionary of English v.0.48:

Extent \Ex*tent"\, a. [L. extentus, p. p. of extendere. See
   Extend.]
   Extended. [Obs.] --Spenser.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Extent \Ex*tent"\, n. [L. extentus, fr. extendere. See
   Extend.]
   1. Space or degree to which a thing is extended; hence,
      superficies; compass; bulk; size; length; as, an extent of
      country or of line; extent of information or of charity.
      [1913 Webster]

            Life in its large extent is scare a span. --Cotton.
      [1913 Webster]

   2. Degree; measure; proportion. "The extent to which we can
      make ourselves what we wish to be." --Lubbock.
      [1913 Webster]

   3. (Eng. Law)
      (a) A peculiar species of execution upon debts due to the
          crown, under which the lands and goods of the debtor
          may be seized to secure payment.
      (b) A process of execution by which the lands and goods of
          a debtor are valued and delivered to the creditor.
          [1913 Webster]

WordNet (r) 3.0 (2006):

extent
    n 1: the point or degree to which something extends; "the extent
         of the damage"; "the full extent of the law"; "to a certain
         extent she was right"
    2: the distance or area or volume over which something extends;
       "the vast extent of the desert"; "an orchard of considerable
       extent"

Moby Thesaurus II by Grady Ward, 1.0:

147 Moby Thesaurus words for "extent":
   acreage, aesthetic distance, ambit, amount, amplitude, area, beam,
   bigness, body, bounds, breadth, broadness, bulk, caliber,
   capaciousness, clearance, compass, continuum, coverage, cut,
   deep space, degree, depth, depths of space, diameter, dimension,
   dimensions, distance, distance across, divergence, domain,
   emptiness, empty space, enormousness, expanse, expansion,
   extension, farness, field, force, fullness, galactic space, gauge,
   girth, grade, greatness, height, immensity, infinite space,
   infinity, interstellar space, interval, largeness, latitude, leap,
   leeway, length, lengthiness, lengths, level, light-years, limit,
   limitation, linear measures, long time, longitude, longness,
   magnitude, margin, mark, mass, matter, measure, measurement,
   mileage, neighborhood, notch, nothingness, nuance, numbers, orbit,
   order, outer space, overall length, parsecs, pas, peg, period,
   perpetuity, perspective, piece, pitch, plane, plateau, point,
   proportion, proportions, province, purview, quantity, quantum,
   radius, range, ratio, reach, region, remoteness, remove, round,
   rung, scale, scope, separation, shade, shadow, size, space,
   spaciousness, span, spatial extension, sphere, spread, stair,
   standard, step, stint, strength, stretch, stride, substance, sum,
   superficial extension, surface, sweep, territory, tract, tread,
   tune, vicinity, void, volume, way, ways, whole, wideness, width,
   yardage