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”
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
Synonyms, antonyms and the broader and narrower relations for vein come from Princeton University’s WordNet. Full sources and licences.