WordNet records no synonym and no antonym for coal tar. 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.
a tar formed from distillation of bituminous coal; coal tar can be further distilled to give various aromatic compounds
Synonyms, antonyms and the broader and narrower relations for coal tar come from Princeton University’s WordNet. Full sources and licences.