passably vs pretty

passably is not an adjective while pretty is an adjective.

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

As adverbs, passably and pretty are synonyms defined as:

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

passably (adjective)	pretty (adjective)
	(used ironically) unexpectedly bad
	pleasing by delicacy or grace; not imposing

passably (adverb)	pretty (adverb)
to certain extent or degree	to certain extent or degree