masking vs concealing

masking and concealing both are nouns.

Word	Noun	Adjective	Verb	Adverb
masking	Yes	No	No	No
concealing	Yes	Yes	No	No

As nouns, concealing is a hypernym of masking; that is, concealing is a word with a broader meaning than masking:

masking: the act of concealing the existence of something by obstructing the view of it
concealing: the activity of keeping something secret

Other hypernyms of masking include concealment, hiding.

masking (noun)	concealing (noun)
the act of concealing the existence of something by obstructing the view of it	the activity of keeping something secret
scenery used to block the audience's view of parts of the stage that should not be seen
the blocking of one sensation resulting from the presence of another sensation

masking (adjective)	concealing (adjective)
	covering or hiding