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"