rein

rein is a Noun

Definition:

[1] The strap of a bridle, fastened to the curb or snaffle on each side, by which the rider or driver governs the horse. This knight laid hold upon his reyne. Chaucer.

[2] Hence, an instrument or means of curbing, restraining, or governing; government; restraint. "Let their eyes rove without rein." Milton. To give rein, To give the rein to, to give license to; to leave withouut restrain. -- To take the reins, to take the guidance or government; to assume control.