WordNet records no synonym and no antonym for issuer. 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 institution that issues something (securities or publications or currency etc.)
Synonyms, antonyms and the broader and narrower relations for issuer come from Princeton University’s WordNet. Full sources and licences.