|Origin:||reregarde, from rere 'behind' (from Latin retro-) + garde 'guard'|
to make a determined effort to prevent a change that you think is bad, although it seems too late to stop it:
They have been fighting a rearguard action to stop a supermarket being built on the land.
if an army fights a rearguard action, it defends itself at the back against an enemy that is chasing it
the group of soldiers who defend the back of an army against an enemy that is chasing it