The strap of a bridle, fastened to the curb or snaffle on each side, by which the rider or driver governs the horse.
Hence, an instrument or means of curbing, restraining, or governing; government; restraint.
To govern or direct with the reins; as, to rein a horse one way or another.
To restrain; to control; to check.
The long strap that passes from the bit to the rider's hands, by which the rider maintains control of the horse.
one of a pair of long straps (usually connected to the bit or the headpiece) used to control a horse
control and direct with or as if by reins; "rein a horse"
stop or slow up one's horse or oneself by or as if by pulling the reins; "They reined in in front of the post office"
stop or check by or as if by a pull at the reins; "He reined in his horses in front of the post office"
Reins are a type of horse tack. A bridle is an arrangement of straps around the horse's head used for riding and driving the animal. A bridle contains a bit (a piece of metal or rubber that is placed in the horse's mouth) attached to reins.