plaster has 10 distinct synonyms spread across 8 of its 11 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 mixture of lime or gypsum with sand and water; hardens into a smooth solid; used to cover walls and ceilings
Synonyms, antonyms and the broader and narrower relations for plaster come from Princeton University’s WordNet. Full sources and licences.
any of several gypsum cements; a white powder (a form of calcium sulphate) that forms a paste when mixed with water and hardens into a solid; used in making molds and sculptures and casts for broken limbs
a medical dressing consisting of a soft heated mass of meal or clay that is spread on a cloth and applied to the skin to treat inflamed areas or improve circulation etc.
a surface of hardened plaster (as on a wall or ceiling)
“there were cracks in the plaster”
adhesive tape used in dressing wounds