Aback means backwards, and survives in the phrase taken by surprise. Taken aback, quite taken aback, she was taken aback.
Outside taken aback the word is dead. The origin is nautical: a sail is taken aback when the wind hits the wrong side and pushes it back against the mast, which stops the ship dead — exactly the effect the phrase describes. Note that it is a- plus back.
1adverbabackBackwards, in the phrase taken aback.
“I was taken aback when my quiet neighbour suddenly started shouting at me.”
aback is a direction.
Old English onbaec is on plus back. The sailing sense of a sail pressed back against the mast gave the modern phrase.
Old English
onbæc
Middle English
abak
English, today
aback
From Middle English abak, from Old English onbæc, equivalent to a + back. Compare West Frisian tebek (“aback”) literally “to/at back”, Swedish tillbaka idem..
Etymology from Wiktionary, CC BY-SA