vent has 10 distinct synonyms spread across 5 of its 7 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 hole for the escape of gas or air
external opening of urinary or genital system of a lower vertebrate
a slit in a garment (as in the back seam of a jacket)
Synonyms, antonyms and the broader and narrower relations for vent come from Princeton University’s WordNet. Full sources and licences.