straw has 9 distinct synonyms spread across 4 of its 7 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.
plant fiber used e.g. for making baskets and hats or as fodder
a variable yellow tint; dull yellow, often diluted with white
a thin paper or plastic tube used to suck liquids into the mouth
cover or provide with or as if with straw
“cows were strawed to weather the snowstorm”
1 of the 7 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for straw.
Synonyms, antonyms and the broader and narrower relations for straw come from Princeton University’s WordNet. Full sources and licences.