WordNet records no synonym and no antonym for reciprocal pronoun. 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 pronoun or pronominal phrase (as `each other') that expresses a mutual action or relationship between the individuals indicated in the plural subject
“The sentence `They cared for each other' contains a reciprocal pronoun”
Synonyms, antonyms and the broader and narrower relations for reciprocal pronoun come from Princeton University’s WordNet. Full sources and licences.