WordNet records no synonym and no antonym for pyrene. 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.
a pale yellow crystalline hydrocarbon C16H10 extracted from coal tar
the small hard nutlet of a drupe or drupelet; the seed and the hard endocarp that surrounds it
Synonyms, antonyms and the broader and narrower relations for pyrene come from Princeton University’s WordNet. Full sources and licences.