Another word that doesn’t mean what you think it does: Harness. You do not “harness” a horse with reins. While harness can be a noun or a verb, neither is correct when referring to reins, which are the straps that go from the horse’s mouth to the rider’s hands and are used for stopping and for directing the horse. “Harness” as a noun refers to the straps and other equipment used to attach the horse to a wheeled vehicle. The verb “harness” refers to putting this equipment on the horse. Putting the reins on a horse who is pulling a conveyance can be considered “harnessing” him in a general sense, but if you are specifically talking about the reins, you would say you were “bridling” him. The bridle is the part of the equipment (which includes the reins) that goes on the head of a horse to be driven or ridden.