vein has 4 distinct synonyms spread across 4 of its 6 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 blood vessel that carries blood from the capillaries toward the heart
“all veins except the pulmonary vein carry unaerated blood”
Synonyms, antonyms and the broader and narrower relations for vein come from Princeton University’s WordNet. Full sources and licences.
a distinctive style or manner
“he continued in this vein for several minutes”
any of the vascular bundles or ribs that form the branching framework of conducting and supporting tissues in a leaf or other plant organ
a layer of ore between layers of rock