WordNet records no synonym and no antonym for referent. 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.
something referred to; the object of a reference
the first term in a proposition; the term to which other terms relate
something that refers; a term that refers to another term
1 of the 4 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for referent.
Synonyms, antonyms and the broader and narrower relations for referent come from Princeton University’s WordNet. Full sources and licences.