believably vs plausibly

believably and plausibly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
believably	No	No	No	Yes
plausibly	No	No	No	Yes

As adverbs, believably and plausibly are synonyms defined as:

believably and plausibly: easy to believe on the basis of available evidence

Other synonyms of believably include credibly, probably.

believably (adverb)	plausibly (adverb)
in a believable manner	easy to believe on the basis of available evidence
easy to believe on the basis of available evidence