Switch on Definition 1 of 3Pro Tip 1/3Literal Action Used to describe the actual action of activating a device manually. Please switch on the heater; it's chilly in here. Pro Tip 2/3Common Devices Often used with everyday devices such as lights and electronics. I just switched on the coffee machine. Pro Tip 3/3Initial Step Implies the first step to making something operational. Remember to switch on the power supply before use.