somewhat vs passably

somewhat and passably both are adverbs.

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

As adverbs, somewhat and passably are synonyms defined as:

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

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