annunciation has 6 distinct synonyms spread across 2 of its 3 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.
a festival commemorating the announcement of the Incarnation by the angel Gabriel to the Virgin Mary; a quarter day in England, Wales, and Ireland
(Christianity) the announcement to the Virgin Mary by the angel Gabriel of the incarnation of Christ
a formal public statement
“the government made an announcement about changes in the drug war”
Synonyms, antonyms and the broader and narrower relations for annunciation come from Princeton University’s WordNet. Full sources and licences.