dawn has 18 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.
an opening time period
“it was the dawn of the Roman Empire”
become clear or enter one's consciousness or emotions
“It dawned on him that she had betrayed him”
appear or develop
“The age of computers had dawned”
become light
“It started to dawn, and we had to get up”
Synonyms, antonyms and the broader and narrower relations for dawn come from Princeton University’s WordNet. Full sources and licences.