The Collaborative International Dictionary of English v.0.48:

Breadth \Breadth\ (br[e^]dth), n. [OE. brede, breede, whence
   later bredette, AS. br[=ae]du, fr. br[=a]d broad. See
   Broad, a.]
   [1913 Webster]
   1. Distance from side to side of any surface or thing;
      measure across, or at right angles to the length; width.
      [1913 Webster]

   2. (Fine Arts) The quality of having the colors and shadows
      broad and massive, and the arrangement of objects such as
      to avoid to great multiplicity of details, producing an
      impression of largeness and simple grandeur; -- called
      also breadth of effect.

            Breadth of coloring is a prominent character in the
            painting of all great masters.        --Weale.
      [1913 Webster]

WordNet (r) 3.0 (2006):

breadth
    n 1: the capacity to understand a broad range of topics; "a
         teacher must have a breadth of knowledge of the subject";
         "a man distinguished by the largeness and scope of his
         views" [syn: breadth, comprehensiveness, largeness]
    2: the extent of something from side to side [syn: width,
       breadth]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "breadth":
   acreage, amount, amplitude, area, beam, bigness, body, broad gauge,
   broad-mindedness, broadness, bulk, caliber, catholicity, compass,
   comprehensiveness, continuum, cosmopolitanism, coverage, degree,
   depth, detail, diameter, dimension, dimensions, distance,
   ecumenicalism, ecumenicism, ecumenicity, ecumenism, emptiness,
   empty space, expanse, expansion, extension, extent, field,
   fullness, galactic space, gamut, gauge, girth, greatness, height,
   infinite space, interstellar space, large-mindedness, largeness,
   latitude, length, liberality, magnitude, mass, measure,
   measurement, noninsularity, nothingness, orbit, outer space,
   proportion, proportions, radius, range, reach, scale, scope, size,
   space, spacious mind, span, spatial extension, sphere, spread,
   stretch, superficial extension, surface, sweep, thickness, tract,
   unbigotedness, unhideboundness, unparochialism, unprovincialism,
   void, volume, wide-mindedness, wideness, width