caducous has 1 distinct synonym spread across 1 of its 1 sense. 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. Its one recorded opposite is persistent.
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.
shed at an early stage of development
“most amphibians have caducous gills”
Synonyms, antonyms and the broader and narrower relations for caducous come from Princeton University’s WordNet. Full sources and licences.