Antonyms for "turn something off" would be "turn something on," "activate," or "start something." These words refer to the opposite action of shutting down, disconnecting, or deactivating something. For instance, turning on the television is the antonym of turning it off. Other antonyms for "turn something off" could be "increase," "hasten," or "intensify," which refer to actions that enhance or speed up a process. Conversely, "slow down," "diminish," or "reduce" could also be antonyms for "turn something off," referring to actions that lower the intensity, speed, or output of an object or system.