be an understudy or alternate for a role
reverse (a direction, attitude, or course of action)
do something in turns
serving or used in place of another
go back and forth; swing back and forth between two states or conditions
occurring by turns; first one and then the other
someone who takes the place of another person
every second one of a series
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
