passably vs fairly

passably and fairly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
passably	No	No	No	Yes
fairly	No	No	No	Yes

As adverbs, passably and fairly are synonyms defined as:

Other synonyms of passably include jolly, middling, moderately, pretty, reasonably, somewhat.

passably (adverb)	fairly (adverb)
to certain extent or degree	without favoring one party, in a fair evenhanded manner
	to certain extent or degree
	in conformity with the rules or laws and without fraud or cheating