Stumped means "taken aback" "surprised"
be stumped informal
to be unable to answer a question or solve a problem because it is too difficult:
be completely stumped I'm completely stumped - how did she manage to escape?
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stumped
[ stuhmpt ]SHOW IPA
See synonyms for stumped on Thesaurus.com
adjective
completely at a loss; perplexed or nonplussed:
The stumped officer could only stare at the strange object, trying to figure out what it might be.
It does not always mean a question is too difficult to answer. This is why you should always refer to 3,4 or 5 dictionaries.