WordNet records no synonym and no antonym for subsistence. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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.
minimal (or marginal) resources for subsisting
“social security provided only a bare subsistence”
a means of surviving
“farming is a hard means of subsistence”
the state of existing in reality; having substance
Synonyms, antonyms and the broader and narrower relations for subsistence come from Princeton University’s WordNet. Full sources and licences.