REIN, noun [Latin retina, retinaculum. If contracted from the Latin, it is from retineo, otherwise from the root of arrest.]
1. The strap of a bridle, fastened to the curb or snaffle on each side, by which the rider of a horse restrains and governs him.
2. The instrument of curbing, restraining or governing; government.
To give the reins, to give license; to leave without restraint.
To take the reins, to take the guidance or government.
REIN, verb transitive
1. To govern by a bridle.
2. To restrain; to control.