: a small device that starts or stops the flow of electricity to something (such as a lamp or a machine) when it is pressed or moved up and down
: a sudden change from one thing to another
: a device for moving the rails of a track so that a train may be turned from one track to another
: to make a change from one thing to another : to start doing or using something that is different
: to make a change from one thing to another by turning or pushing a button or moving a switch, lever, etc.
: to change or replace (something) with another thing
What made you want to look up switch? Please tell us where you read or heard it (including the quote, if possible).