one of a series of teeth on the edge of a wheel that fit between the teeth on the next wheel and cause it to move （齿轮的）轮齿，嵌齿 
- (also cogwheel)
a wheel with a series of teeth on the edge that fit between the teeth on the next wheel and cause it to move （齿轮的）轮齿，嵌齿
Word OriginMiddle English: probably of Scandinavian origin and related to Swedish kugge and Norwegian kug.
Idioms
a cog in the machine/wheel
- (informal)
a person who is a small part of a large organization （大机构中的）小职员，小成员