The Collaborative International Dictionary of English v.0.48:

Breech \Breech\, v. t. [imp. & p. p. Breeched; p. pr. & vb. n.
   Breeching.]
   1. To put into, or clothe with, breeches.
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            A great man . . . anxious to know whether the
            blacksmith's youngest boy was breeched. --Macaulay.
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   2. To cover as with breeches. [Poetic]
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            Their daggers unmannerly breeched with gore. --Shak.
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   3. To fit or furnish with a breech; as, to breech a gun.
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   4. To whip on the breech. [Obs.]
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            Had not a courteous serving man conveyed me away,
            whilst he went to fetch whips, I think, in my
            conscience, he would have breeched me. --Old Play.
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   5. To fasten with breeching.
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The Collaborative International Dictionary of English v.0.48:

Breeching \Breech"ing\, n.
   1. A whipping on the breech, or the act of whipping on the
      breech.
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            I view the prince with Aristarchus' eyes,
            Whose looks were as a breeching to a boy. --Marlowe.
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   2. That part of a harness which passes round the breech of a
      horse, enabling him to hold back a vehicle.
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   3. (Naut.) A strong rope rove through the cascabel of a
      cannon and secured to ringbolts in the ship's side, to
      limit the recoil of the gun when it is discharged.
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   4. The sheet iron casing at the end of boilers to convey the
      smoke from the flues to the smokestack.
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Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "breeching":
   back band, backstrap, bearing rein, bellyband, bit, blinders,
   blinds, bridle, caparison, cavesson, checkrein, cheekpiece,
   chinband, cinch, collar, crownband, crupper, curb, gag swivel,
   girth, hackamore, halter, hames, hametugs, harness, headgear,
   headstall, hip straps, jaquima, jerk line, lines, martingale,
   noseband, pole strap, reins, ribbons, saddle, shaft tug,
   side check, snaffle, surcingle, tack, tackle, trappings, tug,
   winker braces, yoke