registrar has 2 distinct synonyms spread across 1 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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 person employed to keep a record of the owners of stocks and bonds issued by the company
the administrator responsible for student records
someone responsible for keeping records
Synonyms, antonyms and the broader and narrower relations for registrar come from Princeton University’s WordNet. Full sources and licences.