Aback comes from Old English on bæc, combining Old English on from Proto-Germanic ana from Proto-Indo-European h₂en- meaning "in" with Old English bæc from Proto-Indo-European bʰog- meaning "back."
aback (English): Towards the back or rear; backwards; In the rear;...
Definitions
Towards the back or rear; backwards; In the rear;...
Ancestry of “aback”, step by step
aback traces back through two separate lines of ancestry.