The Collaborative International Dictionary of English v.0.48:

Length \Length\ (l[e^]ngth), n. [OE. lengthe, AS. leng[eth], fr.
   lang, long, long; akin to D. lengte, Dan. l[ae]ngde, Sw.
   l[aum]ngd, Icel. lengd. See Long, a. ]
   1. The longest, or longer, dimension of any object, in
      distinction from breadth or width; extent of anything
      from end to end; the longest line which can be drawn
      through a body, parallel to its sides; as, the length of a
      church, or of a ship; the length of a rope or line.
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   2. A portion of space or of time considered as measured by
      its length; -- often in the plural.
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            Large lengths of seas and shores.     --Shak.
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            The future but a length behind the past. --Dryden.
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   3. The quality or state of being long, in space or time;
      extent; duration; as, some sea birds are remarkable for
      the length of their wings; he was tired by the length of
      the sermon, and the length of his walk.
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   4. A single piece or subdivision of a series, or of a number
      of long pieces which may be connected together; as, a
      length of pipe; a length of fence.
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   5. Detail or amplification; unfolding; continuance as, to
      pursue a subject to a great length.
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            May Heaven, great monarch, still augment your bliss
            With length of days, and every day like this.
                                                  --Dryden.
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   6. Distance. [Obs.]
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            He had marched to the length of Exeter. --Clarendon.
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   At length.
      (a) At or in the full extent; without abbreviation; as,
          let the name be inserted at length.
      (b) At the end or conclusion; after a long period. See
          Syn. of At last, under Last.

   At arm's length. See under Arm.
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The Collaborative International Dictionary of English v.0.48:

Length \Length\, v. t.
   To lengthen. [Obs.] --Shak.
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WordNet (r) 3.0 (2006):

length
    n 1: the linear extent in space from one end to the other; the
         longest dimension of something that is fixed in place; "the
         length of the table was 5 feet"
    2: continuance in time; "the ceremony was of short duration";
       "he complained about the length of time required" [syn:
       duration, length]
    3: the property of being the extent of something from beginning
       to end; "the editor limited the length of my article to 500
       words"
    4: size of the gap between two places; "the distance from New
       York to Chicago"; "he determined the length of the shortest
       line segment joining the two points" [syn: distance,
       length]
    5: a section of something that is long and narrow; "a length of
       timber"; "a length of tubing"

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "length":
   aesthetic distance, amplitude, area, at full length, at length,
   at long last, bigness, body, breadth, bulk, caliber, clearance,
   compass, completely, coverage, deep space, depth, depths of space,
   diameter, dimension, dimensions, distance, divergence, duration,
   eventually, exhaustively, expanse, expansion, extension,
   extensively, extent, farness, finally, fully, gauge, girth,
   greatness, height, in detail, infinity, interminably, largeness,
   leeway, light-years, magnitude, margin, mass, measure, measurement,
   mileage, orbit, panorama, parsecs, period, perspective, piece,
   proportion, proportions, purview, radius, range, reach, realm,
   remoteness, scale, scope, separation, size, space, span, spread,
   stretch, stride, term, thoroughly, ultimately, volume, way, ways,
   width