Rein/reɪn/ Definition 1 of 3Pro Tip 1/3Literal Use Used specifically when talking about horse riding or activities involving physical reins. She grabbed the reins tightly as the horse galloped. Pro Tip 2/3Active Guidance Implies actively guiding or steering something, not just holding onto it. During the lesson, the instructor kept a close hand on the reins. Pro Tip 3/3Not Always Literal Can be used metaphorically to describe control in non-equestrian contexts. He kept a tight rein on the project's budget.