alternate

Be an understudy or alternate for a role.

Reverse (a direction, attitude, or course of action).

Do something in turns.

Go back and forth; swing back and forth between two states or conditions.

Exchange people temporarily to fulfill certain jobs and functions.

Of leaves and branches etc; first on one side and then on the other in two ranks along an axis; not paired.

“stems with alternate leaves”

Serving or used in place of another.

Occurring by turns; first one and then the other.

Every second one of a series.

“the cleaning lady comes on alternate Wednesdays”

Someone who takes the place of another person.