"dubiously" in the adverb sense
1. questionably, dubiously
in a questionable and dubious manner
"these were estates his father questionably acquired"
2. doubtfully, dubiously
in a doubtful manner
"Gerald shook his head doubtfully"
Source: WordNet® (An amazing lexical database of English)
Princeton University "About WordNet®."
WordNet®. Princeton University. 2010.
View WordNet® License