(usu in pl) a long line fastened to a bit, by which a rider or driver controls an animal
(usu in pl, but treated as sing. or pl) a long line fastened usu to both sides of a bit, by which a rider or driver controls an animal
a similar device used to restrain a young child
(in pl) controlling or guiding power
the reins of government
draw rein
to bring a horse to a stop while riding
give free rein to/give free rein to something
to allow something to proceed or function freely
[Middle English reine via French from Latin retinēre: see retain]