very important person vs high-up

very important person and high-up both are nouns.

Word	Noun	Adjective	Verb	Adverb
very important person	Yes	No	No	No
high-up	Yes	No	No	No

As nouns, very important person and high-up are synonyms defined as:

very important person and high-up: an important or influential (and often overbearing) person

Other synonyms of very important person include dignitary, high muckamuck, panjandrum, VIP.

very important person (noun)	high-up (noun)
an important or influential (and often overbearing) person	an important or influential (and often overbearing) person