WordNet records no synonym and no antonym for paramount issue. It is the only member of its synset, 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.
an issue whose settlement is more important than anything else; and issue that must be settled before anything else can be settled
Synonyms, antonyms and the broader and narrower relations for paramount issue come from Princeton University’s WordNet. Full sources and licences.