[ noun ] one of a pair of long straps (usually connected to the bit or the headpiece) used to control a horse
[ verb ] stop or check by or as if by a pull at the reins
"He reined in his horses in front of the post office"
[ verb ] 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"
[ noun ] Last name, frequency rank in the U.S. is 11968
[ noun ] any means of control
"he took up the reins of government"