conceal vs mask

conceal is not a noun while mask is a noun.

Word	Noun	Adjective	Verb	Adverb
conceal	No	No	Yes	No
mask	Yes	No	Yes	No

As verbs, mask is a hyponym of conceal; that is, mask is a word with a more specific, narrower meaning than conceal:

conceal (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

conceal (verb)	mask (verb)
hold back; keep from being perceived by others	put a mask on or cover with a mask
prevent from being seen or discovered	shield from light
	cover with a sauce
	hide under a false appearance
	make unrecognizable