cover-up vs blue wall

cover-up and blue wall both are nouns.

Word	Noun	Adjective	Verb	Adverb
cover-up	Yes	No	No	No
blue wall	Yes	No	No	No

As nouns, blue wall is a hyponym of cover-up; that is, blue wall is a word with a more specific, narrower meaning than cover-up:

cover-up: concealment that attempts to prevent something scandalous from becoming public
blue wall: the secrecy of police officers who lie or look the other way to protect other police officers

Other hyponyms of cover-up include blue wall of silence, wall of silence.

cover-up (noun)	blue wall (noun)
concealment that attempts to prevent something scandalous from becoming public	the secrecy of police officers who lie or look the other way to protect other police officers