Rein meaning

one of a pair of long straps (usually connected to the bit or the headpiece) used to control a horse

any means of control

“he took up the reins of government”

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”

keep in check

“rule one's temper”