Synonyms of the word 
CREDIBLY → BELIEVABLY - PLAUSIBLY - PROBABLY
credibly
- adv. In a credible manner; believably.
- adv. Used to report the speaker's assessment of the credibility of a reported statement.
believably
- adv. In a believable way.
- adv. Used to express the speaker's assessment of the credibility of a reported statement.
plausibly
- adv. (manner) In a plausible manner.
- adv. (modal) Not falsifiably, based on available facts and general knowledge.
probably
- adv. In all likelihood.
If you are interested in words, visit the following sites :
- wiktionary.org/credibly For complete definition of a word
- 1word.ws/credibly to play with words, suffixs, prefixs, etc.