passably vs somewhat

passably and somewhat both are adverbs.

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

As adverbs, passably and somewhat are synonyms defined as:

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

passably (adverb)	somewhat (adverb)
to certain extent or degree	to certain extent or degree
	to a small degree or extent