terret
One of the rings on the top of the harness saddle, through which the reins pass.
She had a good idea of what was coming, and the moment York took the rein off the terret in order to shorten it, she took her opportunity, and reared up so suddenly, that York had his nose roughly hit, and his hat knocked off; […]
Where it comes from
Alteration of Middle English toret, turret (“half-ring, eyelet”), from Anglo-Norman turette, diminutive of Old French tur (“circuit, ring”). More at turn.
Adapted from the Wiktionary entry terret (CC BY-SA 4.0).