Rein

1. A long, narrow leather strap attached to each side of the bit of a bridle used by a rider or driver to control a horse or other animal. You should learn how to properly use the reins.
2. A means or restraint, check, or guidance. She needs to rein in her loud vocal objections.
3. Often reins. A means or an instrument by which power is exercised. Our lives are often in the hands of the reins of government.
4. To release from constraints. allow to go unchecked. She gave rein to her emotions.
5. Close control. He kept expenses on a tight rein.