Meaning of ABACK in English
adv. 1 archaic backwards, behind. 2 Naut. (of a sail) pressed against the mast by a head wind. take aback 1 surprise, disconcert (your request took me aback; I was greatly taken aback by the news). 2 (as taken aback) (of a ship) with the sails pressed against the mast by a head wind.
[ OE on bc (as A(2), BACK) ]
Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012