open up vs gap

open up is not a noun while gap is a noun.

Word	Noun	Adjective	Verb	Adverb
open up	No	No	Yes	No
gap	Yes	No	Yes	No

As verbs, gap is a hyponym of open up; that is, gap is a word with a more specific, narrower meaning than open up:

Other hyponyms of open up include unbar, break open, click open, reopen, unlock, unbolt, unseal, uncork, jimmy, lever, prise, prize, pry, breach, lance.

open up (noun)	gap (noun)
	an act of delaying or interrupting the continuity
	a narrow opening
	a conspicuous disparity or difference as between two figures
	a difference (especially an unfortunate difference) between two opinions or two views or two situations
	an open or empty space in or between things
	a pass between mountain peaks; geomorphological term for the lowest point on a mountain ridge between two peaks

open up (verb)	gap (verb)
make available	make an opening or gap in
become available
talk freely and without inhibition
cause to open or to become open
become open
open up an area or prepare a way
start to operate or function or cause to start operating or functioning