take someone aback shock, surprise, or disconcert someone.
☞ The phrase is frequently used in the passive form (be taken aback): this was adopted in the mid 19th century from earlier (mid 18th-century) nautical terminology, to describe the situation of a ship with its sails pressed back against the mast by a headwind, preventing forward movement.
1991Kathleen JonesLearning Not To Be First They were taken aback by the shabbiness of the hotel and lack of cleanliness in the city generally.