The antonyms of "reins in" are "let go," "loose," "release," and "uncork." When someone "reins in" something, they are exercising control or restraint over it. Opposingly, when someone "lets go" or "loosens" something, they are relinquishing control and allowing it to be free. Similarly, when something is "released" or "uncorked," it is freed from its confinement or limitations. These antonyms are often used in situations where it is necessary to let things or events unfold naturally without restrictions or limitations. Therefore, it is essential to recognize the context in which these antonyms are used to avoid confusion or misunderstanding.