A strap or rope attached to a bridle or bit, used to control a horse, animal or young child.

(figurative) An instrument or means of curbing, restraining, or governing.

(now rare, archaic, chiefly in plural) A kidney.

The inward impulses; the affections and passions, formerly supposed to be located in the area of the kidneys.

(transitive) To direct or stop a horse by using reins.

(transitive) To restrain; to control; to check.

(intransitive) To obey directions given with the reins.