RE:
what is the definition of taken aback?
well here i will use it in a sentance

"But it's all nonsense". said edmund very TAKEN ABACK.

Ex.

I am taken aback that you have done such a thing.

For example:

“When Martha opened her credit card bill, she was taken aback by the huge finance charges”.

It also has another aspect to it, which is that the person who is “taken aback” is caused to rethink his whole position on a thing… his former, forward steps of thought are now sent back to square one. 🙁

Bewildered.

Context example: She was taken aback at the thought that he had access to the internet, yet couldn’t do his own search! 😉