countable/uncountable the part of an engine that changes engine power into movement. Most cars in the U.S. are automatics, so the engine changes between gears without the driver having to do anythingchange gears: Helen changed gears as she approached the intersection.
first/second/third etc. gear: I put the car into fourth gear when I got onto the highway.
low/high gear: Always use a low gear when driving down a steep hill.
grind the gears (=make a noise when changing gear because you do not do it correctly): You’ll ruin the transmission if you keep grinding the gears like that.
in gear (=with one of the gears connected so that the power of the engine will make the wheels move): The car won’t move unless you’re in gear.
out of gear (=with no gears connected): Take the car out of gear.