1. a valve in a toilet tank that is controlled by a floating ball and automatically shuts off the water supply when the tank is full
Usage: also called a ball valve or float valve; common in plumbing

Examples

• The ballcock in the toilet tank needs to be replaced because water keeps running.
• When you flush, the ballcock drops and allows fresh water to refill the tank.
• A faulty ballcock can cause the toilet to overflow.
• The plumber adjusted the ballcock to fix the water level in the tank.
• Modern ballcocks are more efficient than older models.