existence has 8 distinct synonyms spread across 2 of its 2 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 nonexistence.
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 state or fact of existing
“a point of view gradually coming into being”
everything that exists anywhere
“they study the evolution of the universe”
Synonyms, antonyms and the broader and narrower relations for existence come from Princeton University’s WordNet. Full sources and licences.