vegetation has 2 distinct synonyms spread across 1 of its 4 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 abnormal growth or excrescence (especially a warty excrescence on the valves of the heart)
inactivity that is passive and monotonous, comparable to the inactivity of plant life
“their holiday was spent in sleep and vegetation”
Synonyms, antonyms and the broader and narrower relations for vegetation come from Princeton University’s WordNet. Full sources and licences.