COMMON If you give someone free rein or give someone a free rein, you give them all the freedom they want or need to do something. Note: The reference in these expressions is to a rider using the reins to control a horse. He was given free rein to manage the project as he wished. Much to her delight, she was given a free rein to decorate the house exactly as she wanted. Note: You can also say that you allow someone free reign. The artists were allowed free rein to produce what they thought fitted the space. Note: You can also say that you have free rein. The children have free rein to choose the subjects that they want to study.