Harness, n.
Etymology: [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. Gf. Iron.]
1. Originally, the complete dress, especially in a military sense, of a man or a horse; hence, in general, armor. At least we 'll die witch harness on our back. Shak.
2. The equipment of a draught or carriage horse, for drawing a wagon, coach, chaise, etc.; gear; tackling.
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. To die in harness, to die with armor on; hence, colloquially, to die while actively engaged in work or duty.
1 other Webster entry under this spelling
Harness, v. t. [imp. & p. p. Harnessed; p. pr. & vb. n. Harnessing.]
1. To dress in armor; to equip with armor for war, as a horseman; to array. Harnessed in rugged steel. Rowe. A gay dagger, Harnessed well and sharp as point of spear. Chaucer.
2. Fig.: To equip or furnish for defense. Dr. H. More.
3. To make ready for draught; to equip with harness, as a horse. Also used figuratively. Harnessed to some regular profession. J. C. Shairp. Harnessed antelope. (Zoöl.) See Guib. -- Harnessed moth (Zoöl.), an American bombycid moth (Arctia phalerata of Harris), having, on the fore wings, stripes and bands of buff on a black ground.
Shades of meaning
Fernald has no entry of its own for harness; he lists it under arms, caparison.
Where he writes about it:
Harness was formerly used of the armor of a knight as well as of a horse; it is now used almost exclusively of the straps and appurtenances worn by a horse when attached to a vehicle; the animal is said to be "kind in harness." The other words apply to the ornamental outfit of a horse, especially under saddle. — from caparison