The past tense of "be taken aback" is "was taken aback" or "were taken aback," depending on the subject.
"He was taken 'aback' by the story he heard"
Taken aback
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.
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aghast....taken aback....tight-lipped...
I was momentarily taken aback by the kitten's sudden defiance.
She was taken aback by his unassuming demeanor, not expecting such humility from someone of his stature.
I was momentarily taken aback when the ploice officer said, "Catch you later."
Scheduling conflicts BUT there is a rumor that they met on the studio lot and she was taken aback by all of Elvis' Memphis Mafia members
He was taken aback as he feared that they would kill him, for killing a Egyptian.
I was suddenly taken aback by quite an unusual sight. That's an unusual design.