gear

/gɪr/

a toothed wheel that engages another toothed mechanism in order to change the speed or direction of transmitted motion

中文释义：齿轮；传动装置

The machine's gears need to be oiled regularly to prevent wear.

机器的齿轮需要定期上油以防止磨损。

He shifted gears smoothly as the car climbed the hill.

汽车爬坡时他平稳地换挡。