noun

• (figurative) An instrument or means of curbing, restraining, or governing.
  "The government is attempting to keep a rein on rising prices."

verb

• (transitive) To direct or stop a horse by using reins.
  "He mounts and reins his horse."
• (transitive) To restrain; to control; to check.
  "Being once chafed, he cannot / Be reined again to temperance."
• (intransitive) To obey directions given with the reins.
  "She worked each horse at a walk, trot, and then a canter. The horses reined well and executed stops quickly."

noun

• (now rare, archaic, chiefly in plural) A kidney.
  "a man subject to these like imaginations[…]hath often the stone imaginarily, before he have it in his reines[…]."

noun

• (telecommunications) Acronym of repetitive electrical impulse noise.