(idiomatic) To be in charge, to be in control, as of a business, political organization, or other group.

(intransitive) To bring a ridden animal to a halt by pulling on the reins. / (transitive) To fit reins on (a horse) / (transitive) To stop, to cause to come to a halt.

A checkrein.

plural of bearing rein

A rein for drawing the bit upward in the horse's mouth.

A rein used to lead an animal (especially a horse) when there is no rider, or when the rider is young or inexperienced.

plural of leading rein

plural of gag rein

The separate rein used to control a bridoon.

plural of bridoon rein