middling vs pretty

middling is a noun but pretty is not a noun.

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

As adverbs, middling and pretty are synonyms defined as:

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

middling (noun)	pretty (noun)
any commodity of intermediate quality or size (especially when coarse particles of ground wheat are mixed with bran)

middling (adjective)	pretty (adjective)
lacking exceptional quality or ability	(used ironically) unexpectedly bad
	pleasing by delicacy or grace; not imposing

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