yam has 1 distinct synonym 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.
sweet potato with deep orange flesh that remains moist when baked
edible tuberous root of various yam plants of the genus Dioscorea grown in the tropics world-wide for food
Synonyms, antonyms and the broader and narrower relations for yam come from Princeton University’s WordNet. Full sources and licences.