I. adverb 1.
‹archaic› towards or situated to the rear; back.
• the little strip of pasture aback of the house.
[Sailing] with the sail pressed backwards against the mast by a headwind.
• Peter holds the jib aback until our bow swings across the wind.
II. phrases take someone aback shock or surprise someone • he was taken aback by her directness.
– origin Old English on bæc (see a-2, back). The term came to be treated as a single word in nautical use.