rumen has 1 distinct synonym spread across 1 of its 1 sense. 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.
the first compartment of the stomach of a ruminant; here food is collected and returned to the mouth as cud for chewing
Synonyms, antonyms and the broader and narrower relations for rumen come from Princeton University’s WordNet. Full sources and licences.