mask has 7 distinct synonyms spread across 4 of its 9 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is unmask.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
put a mask on or cover with a mask
“Mask the children for Halloween”
Synonyms, antonyms and the broader and narrower relations for mask come from Princeton University’s WordNet. Full sources and licences.
a covering to disguise or conceal the face
activity that tries to conceal something
“no mask could conceal his ignorance”
a party of guests wearing costumes and masks
a protective covering worn over the face