"believably" in the adverb sense
1. believably
in a believable manner
"he acted believably sincere"
2. credibly, believably, plausibly, probably
easy to believe on the basis of available evidence
"he talked plausibly before the committee"
"he will probably win the election"
Source: WordNet® (An amazing lexical database of English)
Princeton University "About WordNet®."
WordNet®. Princeton University. 2010.
View WordNet® License