The Collaborative International Dictionary of English v.0.48:

Harness \Har"ness\ (-n[e^]s), n. [OE. harneis, harnes, OF.
   harneis, F. harnais, harnois; of Celtic origin; cf. Armor.
   harnez old iron, armor, W. haiarn iron, Armor. houarn, Ir.
   iarann, Gael. iarunn. Cf. Iron.]
   1. Originally, the complete dress, especially in a military
      sense, of a man or a horse; hence, in general, armor.
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            At least we'll die with harness on our back. --Shak.
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   2. The equipment of a draught or carriage horse, for drawing
      a wagon, coach, chaise, etc.; gear; tackling.
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   3. The part of a loom comprising the heddles, with their
      means of support and motion, by which the threads of the
      warp are alternately raised and depressed for the passage
      of the shuttle.
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   To die in harness, to die with armor on; hence,
      colloquially, to die while actively engaged in work or
      duty.
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The Collaborative International Dictionary of English v.0.48:

Harness \Har"ness\, v. t. [imp. & p. p. Harnessed (-n[e^]st);
   p. pr. & vb. n. Harnessing.] [OE. harneisen; cf. F.
   harnacher, OF. harneschier.]
   1. To dress in armor; to equip with armor for war, as a
      horseman; to array.
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            Harnessed in rugged steel.            --Rowe.
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            A gay dagger,
            Harnessed well and sharp as point of spear.
                                                  --Chaucer.
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   2. Fig.: To equip or furnish for defense. --Dr. H. More.
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   3. To make ready for draught; to equip with harness, as a
      horse. Also used figuratively.
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            Harnessed to some regular profession. --J. C.
                                                  Shairp.
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   Harnessed antelope. (Zool.) See Guib.

   Harnessed moth (Zool.), an American bombycid moth (Arctia
      phalerata of Harris), having, on the fore wings, stripes
      and bands of buff on a black ground.
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WordNet (r) 3.0 (2006):

harness
    n 1: a support consisting of an arrangement of straps for
         holding something to the body (especially one supporting a
         person suspended from a parachute)
    2: stable gear consisting of an arrangement of leather straps
       fitted to a draft animal so that it can be attached to and
       pull a cart
    v 1: put a harness; "harness the horse" [syn: harness,
         tackle] [ant: unharness]
    2: exploit the power of; "harness natural forces and resources"
    3: control and direct with or as if by reins; "rein a horse"
       [syn: harness, rein in, draw rein, rein]
    4: keep in check; "rule one's temper" [syn: rule, harness,
       rein]