endemic has 6 distinct synonyms spread across 3 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. Its 3 recorded opposites are epidemic, ecdemic, cosmopolitan.
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.
native to or confined to a certain region
“the islands have a number of interesting endemic species”
originating where it is found
“the autochthonal fauna of Australia includes the kangaroo”
a disease that is constantly present to a greater or lesser degree in people of a certain class or in people living in a particular location
a plant that is native to a certain limited area
“it is an endemic found only this island”
Synonyms, antonyms and the broader and narrower relations for endemic come from Princeton University’s WordNet. Full sources and licences.