third wheel

big wheel

A person with a great deal of power or influence, especially a high-ranking person in an organization.

break the wheel

To end a pattern of oppression, inequality, injustice, or abuse.

fifth wheel

Anything superfluous or unnecessary.

hamster wheel

To cycle fruitlessly.

reinvent the wheel

To do work unnecessarily when it has already been done satisfactorily by others; to attempt to devise a solution to a problem when a solution already exists.

set one's shoulder to the wheel

Synonym of put one's shoulder to the wheel.

take the wheel

To assume control of a situation.

third hand

Not new, having more than one previous owner.