surcingle

noun

1. A long unpadded strap to pass over and keep in place a blanket, pack or saddle on an animal.

   “He was standing on the offside of his horse, holding up the flap of his saddle, with the surcingle loosened, and was pointing to the girths. Close to their attachment to the saddle they had been almost cut through with a knife.”

2. A piece of tack wrapped around the belly of a horse, to use when longeing.
3. A girdle to fasten a garment, especially a cassock.

verb

1. (transitive)To fasten with a surcingle.