western vs midwestern

western is a noun but midwestern is not a noun.

Word	Noun	Adjective	Verb	Adverb
western	Yes	Yes	No	No
midwestern	No	Yes	No	No

western (noun)	midwestern (noun)
a sandwich made from a western omelet

western (adjective)	midwestern (adjective)
relating to or characteristic of the western parts of the world or the West as opposed to the eastern or oriental parts	of a region of the United States generally including Ohio, Indiana, Illinois, Iowa, Missouri, Kansas, Nebraska, and sometimes Michigan, Wisconsin, Minnesota
of or characteristic of regions of the United States west of the Mississippi River
lying toward or situated in the west
of wind; from the west