Meaning of "gear" in Essential English Dictionary

gear

noun uk /ɡɪər/

the parts in a car or bicycle that control how fast the wheels turn:

I have a mountain bike with 21 gears.
I changed gear.
first, second, third, etc. gear

a particular position of the gears in a car, bicycle, etc. that controls how fast the wheels turn:

I left the car in first gear.

[ no plural ] the clothes and things that you use for a particular purpose:

sports gear

(Definition of “gear” from the Cambridge Essential Dictionary © Cambridge University Press)