Other forms: unmasked, unmasking, unmasks
To unmask is to reveal who somebody really is. Unmask the impostor, unmasked at last, unmask the culprit.
It is theatrical by origin and figurative in nearly every use — what is unmasked is a pretence rather than a face. It suits fraud, spies and villains in fiction. Note that the un- here undoes an action rather than negating a state, as in untie and unlock, which is a distinct use of the prefix.
1verbunmaskTo reveal who somebody really is.
“The investigation unmasked the charity's director as a fraud.”
unmask is a revealing.
Un- plus mask, where un- undoes the action. Untie and unlock use the same reversing prefix.
Proto-West Germanic
*maskā
Medieval Latin
masca
Italian
maschera — mask, disguise
Middle French
masque — a covering to hide or protect the face
English
mask
English, today
unmask
From un + mask. Compare typologically reveal (see more). mask Borrowed from Middle French masque (“a covering to hide or protect the face”), from Italian maschera (“mask, disguise”), from (a byform of, see it for more) Medieval Latin masca, mascha, a borrowing of Proto-West Germanic maskā, from which English a doublet of mesh and a doublet of are inherited. a doublet of mascara and masque and mesh. Replaced Old English grīma (“mask”), whence grime, and displaced non-native Middle English viser (“visor, mask”) borrowed from Old French viser, visier.
Etymology from Wiktionary, CC BY-SA