What is "to give the rein to"

Rein \Rein\ (r?n), n. [F. r[^e]ne, fr. (assumed) LL. retina, fr. L. retinere to hold back. See Retain.]

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.