facultative has 1 distinct synonym spread across 1 of its 4 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 one recorded opposite is obligate.
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.
able to exist under more than one set of conditions
“a facultative parasite can exist as a parasite or a saprophyte”
2 of the 4 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for facultative.
Synonyms, antonyms and the broader and narrower relations for facultative come from Princeton University’s WordNet. Full sources and licences.