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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