Meaning

noun a support consisting of an arrangement of straps for holding something to the body (especially one supporting a person suspended from a parachute)

noun 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

verb put a harness

originFrom Middle English harneys, harnes, harneis, harnais, herneis, from Anglo-Norman harneis and Old French hernois (“equipment used in battle”), believed to be from Old Norse *hernest, from herr (“army”) + nest (“provisions”) (from Proto-Germanic *nesaną (“to heal, recover”)). More at harry.

Etymology from Wiktionary, CC BY-SA 3.0