The past tense of "be taken aback" is "wastaken aback".
Example: "She was taken aback by the amazing fireworks."
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"He was taken 'aback' by the story he heard"
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aback is having the wind against the forward side of the
sails.
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It is a nautical term. When the sails of a squared-rigged
sailing ship are suddenly carried by the wind back against the mast
the ship is 'taken aback' and stopped dead. So that lead to a
person being taken aback as well.