ventilate has 4 distinct synonyms spread across 2 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.
expose to the circulation of fresh air so as to retard spoilage
“Wheat should be well ventilated”
circulate through and freshen
“The gust of air ventilated the room”
furnish with an opening to allow air to circulate or gas to escape
“The architect did not think about ventilating the storage space”
Synonyms, antonyms and the broader and narrower relations for ventilate come from Princeton University’s WordNet. Full sources and licences.