ply has 4 distinct synonyms spread across 2 of its 8 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.
one of the strands twisted together to make yarn or rope or thread; often used in combination
“three-ply cord”
(usually in combinations) one of several layers of cloth or paper or wood as in plywood
Synonyms, antonyms and the broader and narrower relations for ply come from Princeton University’s WordNet. Full sources and licences.