rein
noun
[ reɪn ]
• a long, narrow strap attached at one end to a horse's bit, typically used in pairs to guide or check a horse in riding or driving.
rein
verb
• check or guide (a horse) by pulling on its reins.
• "he reined in his horse and waited"
Origin:
Middle English: from Old French rene, based on Latin retinere ‘retain’.