mantle has 13 distinct synonyms spread across 6 of its 10 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.
the cloak as a symbol of authority
“place the mantle of authority on younger shoulders”
United States baseball player (1931-1997)
the layer of the earth between the crust and the core
shelf that projects from wall above fireplace
hanging cloth used as a blind (especially for a window)
Synonyms, antonyms and the broader and narrower relations for mantle come from Princeton University’s WordNet. Full sources and licences.