The antonyms for the word "re-lax" are keeping busy, exerting oneself, tensing up, and stressing out. Keeping busy means engaging in activities that require physical or mental exertion, which may not be relaxing, while exerting oneself signifies putting in a lot of effort to achieve a specific goal. Tensing up refers to the state of muscular contraction that can happen when someone is anxious or nervous. Stressing out means experiencing pressure, anxiety, or tension that can come from various sources such as work, relationships, or financial issues. Overall, the opposite of relaxing involves activities that require effort, mental or physical, and can be stressful or pressurizing.