marrow has 17 distinct synonyms spread across 5 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.
the fatty network of connective tissue that fills the cavities of bones
any of various squash plants grown for their elongated fruit with smooth dark green skin and whitish flesh
large elongated squash with creamy to deep green skins
Synonyms, antonyms and the broader and narrower relations for marrow come from Princeton University’s WordNet. Full sources and licences.