The Collaborative International Dictionary of English v.0.48:

Depth \Depth\ (s[e^]pth), n. [From Deep; akin to D. diepte,
   Icel. d[=y]pt, d[=y]p[eth], Goth. diupi[thorn]a.]
   1. The quality of being deep; deepness; perpendicular
      measurement downward from the surface, or horizontal
      measurement backward from the front; as, the depth of a
      river; the depth of a body of troops.
      [1913 Webster]

   2. Profoundness; extent or degree of intensity; abundance;
      completeness; as, depth of knowledge, or color.
      [1913 Webster]

            Mindful of that heavenly love
            Which knows no end in depth or height. --Keble.
      [1913 Webster]

   3. Lowness; as, depth of sound.
      [1913 Webster]

   4. That which is deep; a deep, or the deepest, part or place;
      the deep; the middle part; as, the depth of night, or of
      winter.
      [1913 Webster]

            From you unclouded depth above.       --Keble.
      [1913 Webster]

            The depth closed me round about.      --Jonah ii. 5.
      [1913 Webster]

   5. (Logic) The number of simple elements which an abstract
      conception or notion includes; the comprehension or
      content.
      [1913 Webster]

   6. (Horology) A pair of toothed wheels which work together.
      [R.]
      [1913 Webster]

   7. (A["e]ronautics) The perpendicular distance from the chord
      to the farthest point of an arched surface.
      [Webster 1913 Suppl.]

   8. (Computers) the maximum number of times a type of
      procedure is reiteratively called before the last call is
      exited; -- of subroutines or procedures which are
      reentrant; -- used of call stacks.
      [PJC]

   Depth of a sail (Naut.), the extent of a square sail from
      the head rope to the foot rope; the length of the after
      leach of a staysail or boom sail; -- commonly called the
      drop of a sail.
      [1913 Webster]

WordNet (r) 3.0 (2006):

depth
    n 1: the extent downward or backward or inward; "the depth of
         the water"; "depth of a shelf"; "depth of a closet" [syn:
         depth, deepness]
    2: degree of psychological or intellectual profundity
    3: (usually plural) the deepest and most remote part; "from the
       depths of darkest Africa"; "signals received from the depths
       of space"
    4: (usually plural) a low moral state; "he had sunk to the
       depths of addiction"
    5: the intellectual ability to penetrate deeply into ideas [syn:
       astuteness, profundity, profoundness, depth,
       deepness]
    6: the attribute or quality of being deep, strong, or intense;
       "the depth of his breathing"; "the depth of his sighs," "the
       depth of his emotion"

Moby Thesaurus II by Grady Ward, 1.0:

139 Moby Thesaurus words for "depth":
   French pitch, Sophia, abstruseness, abysm, abyss, acumen,
   amplitude, area, astuteness, bigness, bodily size, body,
   bottomless pit, brain, breadth, brightness, brilliance, brilliancy,
   broad-mindedness, bulk, caliber, cavity, chasm, classical pitch,
   coarseness, complexity, comprehensively, corpulence, coverage,
   crater, crevasse, deep, deeply, deepness, deeps, depths, diameter,
   dimension, dimensions, distance through, draft, drop, erudition,
   expanse, expansion, extension, extensively, extent, fatness, gauge,
   girth, good understanding, greatness, grossness, gulf, height,
   high pitch, hole, hollow, in detail, innerness, inness, insight,
   intellect, intelligence, intensity, intensively, interiority,
   internality, internalization, intricacy, intrinsicality,
   introversion, intuition, inwardness, keenness, key, largeness,
   length, low pitch, lowness, magnitude, mass, measure, measurement,
   mellow wisdom, nadir, new philharmonic pitch, note, obscurity,
   penetration, perception, perspicaciousness, perspicacity,
   philharmonic pitch, philosophical pitch, pit, pitch, profoundly,
   profoundness, profundity, proportion, proportions, radius, range,
   reach, reconditeness, register, richness, ripe wisdom, sagacity,
   sageness, sapience, scale, scope, seasoned understanding, sense,
   shaft, sharpness, size, sound understanding, sounding, spread,
   standard pitch, strength, the third dimension, thickness,
   thoroughly, tonality, tone, tune, understanding, vividness, volume,
   well, width, wisdom, wiseness, yawning abyss