WordNet records no synonym and no antonym for moderator. 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.
any substance used to slow down neutrons in nuclear reactors
in the Presbyterian church, the officer who presides over a synod or general assembly
someone who presides over a forum or debate
Synonyms, antonyms and the broader and narrower relations for moderator come from Princeton University’s WordNet. Full sources and licences.