somewhat vs middling

somewhat is not a noun while middling is a noun.

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

As adverbs, somewhat and middling are synonyms defined as:

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

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

somewhat (adjective)	middling (adjective)
	lacking exceptional quality or ability

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