Aback (adverb)

Taken unawares or by surprise; in a state of unpreparedness.

Origin:

Middle english abak, from old english on bæc; akin to old high german bah back and probably to old english bæc, bæce back.

Examples:

1. She was taken aback by his rude behavior.
2. He was caught aback by the news.
3. The proposal took her aback.
4. The sudden noise caught me aback.
5. The change in plans caught them aback.