colloquialism vs high-flown

colloquialism is a noun but high-flown is not a noun.

Word	Noun	Adjective	Verb	Adverb
colloquialism	Yes	No	No	No
high-flown	No	Yes	No	No

colloquialism (noun)	high-flown (noun)
a colloquial expression; characteristic of spoken or written communication that seeks to imitate informal speech

colloquialism (adjective)	high-flown (adjective)
	of high moral or intellectual value; elevated in nature or style
	pretentious (especially with regard to language or ideals)