De-activates refers to the act of disabling or turning off something. Its antonyms include activate, switch on, enable, turn on, energize, ignite, start up, and power up. The opposite of de-activating is to put something into operation. For example, you can activate a security system, switch on a device or appliance, energize the lights, or ignite a gas stove. These antonyms are useful in various situations, such as when you want to start using a piece of equipment or power up a machine. By knowing the opposite of de-activating, you can easily use the right words to describe what you want to accomplish.