The word discharge has several meanings:

1. To release or let go of something that was contained or held. A hospital discharges a patient when they're well enough to go home. A soldier receives a discharge from the military when their service ends. A factory might discharge waste into a river (though environmental laws now restrict this). The word suggests something that was previously held, stored, or contained is now being let out or released.
2. To fire or shoot, especially a weapon or electricity. When you discharge a firearm, you pull the trigger and fire it. Lightning discharges electrical energy from clouds to the ground in a bright flash. A battery discharges when it releases its stored energy to power a device. The noun form describes this release: “the discharge of a gun” or “an electrical discharge.”
3. To fulfill a duty or obligation. When you discharge your responsibilities, you complete what you're supposed to do. A judge might discharge their duties by conducting fair trials. A student discharges their homework obligation by finishing and turning in the assignment.

All these meanings share the idea of releasing, completing, or letting something go that was previously held or required.