block out vs mask

block out is not a noun while mask is a noun.

Word	Noun	Adjective	Verb	Adverb
block out	No	No	Yes	No
mask	Yes	No	Yes	No

As verbs, block out and mask are synonyms defined as:

block out (noun)	mask (noun)
	activity that tries to conceal something
	a covering to disguise or conceal the face
	a protective covering worn over the face
	a party of guests wearing costumes and masks

block out (verb)	mask (verb)
plan where and when songs should be inserted into a theatrical production, or plan a theatrical production in general	put a mask on or cover with a mask
indicate roughly	shield from light
shield from light	cover with a sauce
prevent from entering	hide under a false appearance
	make unrecognizable