denial has 8 distinct synonyms spread across 3 of its 5 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.
the act of refusing to comply (as with a request)
“it resulted in a complete denial of his privileges”
the act of asserting that something alleged is not true
(psychiatry) a defense mechanism that denies painful thoughts
renunciation of your own interests in favor of the interests of others
a defendant's answer or plea denying the truth of the charges against him
“he gave evidence for the defense”
Synonyms, antonyms and the broader and narrower relations for denial come from Princeton University’s WordNet. Full sources and licences.