To deactivate something means to turn it off or make it stop working, often by switching off its power or disabling its active functions. When you deactivate a phone app, you stop it from running in the background. A bomb squad might carefully deactivate an explosive device by cutting the wires that would trigger it. Scientists might deactivate a virus in a lab to make it harmless for study.

The word suggests deliberately stopping something that was designed to be active or powerful, often through a purposeful process rather than a simple on-off switch. A soldier might deactivate a security system before entering a building. A doctor might use medicine to deactivate harmful bacteria in your body. When you deactivate your social media account, you're telling the company to make it inactive without deleting it completely, so you could reactivate it later if you wanted.

The opposite of deactivate is activate: to turn something on or make it work. Think of deactivation as putting something into a dormant or sleeping state where it exists but isn't doing anything. A deactivated robot sits silent and still, ready to activate again when someone powers it back up.