thatch has 5 distinct synonyms spread across 2 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.
hair resembling thatched roofing material
plant stalks used as roofing material
an English pirate who operated in the Caribbean and off the Atlantic coast of North America (died in 1718)
Synonyms, antonyms and the broader and narrower relations for thatch come from Princeton University’s WordNet. Full sources and licences.