‘Reign over’ vs. ‘Rein in’
‘Reign over’ means to rule over something or someone. Ex: The queen reigned over the country for over 3 decades. Reign can be used as a noun (as in the period of rule, rule, power) or as a verb (to possess or exercise power).
‘Rein in’ means to stop or control by pulling on the reins. Ex: I don’t know how to rein him in. Reins are leather straps which are used to control horses and animals. Any means of curbing or controlling are also called as reins (noun). Rein used as a verb means to curb, restrain, control. Ex: I am figuring out how to rein in the chaos.