rein

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"