mask vs unmask

mask is a noun but unmask is not a noun.

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

mask (noun)	unmask (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

mask (verb)	unmask (verb)
put a mask on or cover with a mask	reveal the true nature of
shield from light	take the mask off
cover with a sauce
hide under a false appearance
make unrecognizable