pass off has 14 distinct synonyms spread across 3 of its 6 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
be accepted as something or somebody in a false character or identity
“She passed off as a Russian agent”
disregard
“She passed off the insult”
cause to be circulated and accepted in a false character or identity
“She passed the glass off as diamonds”
come to pass
“What is happening?”
Synonyms, antonyms and the broader and narrower relations for pass off come from Princeton University’s WordNet. Full sources and licences.