When you have free rein, you have full and unbridled control or freedom ^{2 1 3}. The expression is often followed by “to,” as in, “I have free rein to design the website” or “The substitute teacher gave the kids free rein to talk during class” ². The term ‘rein’ here refers to the straps that guide a horse’s movement, so ‘free rein’ means ‘to give someone freedom’ in the same way that holding the reins loosely gives a horse freedom to move ³.