rearguard

Etymology

Came into English from Middle English rier garde, which came from Anglo-Norman reregard, reregarde, rereguarde and Middle French rieregarde, in turn from Old French rereguarde (attested in The Song of Roland, c. 1150), formed from rere (“after; behind”) and guarde (“guard”). Taken at face value it can be broken down as rear + guard, and it is a piecewise doublet of retrogarde.