reduplication has 2 distinct synonyms spread across 2 of its 4 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.
repetition of the final words of a sentence or line at the beginning of the next
the syllable added in a reduplicated word form
a word formed by or containing a repeated syllable or speech sound (usually at the beginning of the word)
the act of repeating over and again (or an instance thereof)
Synonyms, antonyms and the broader and narrower relations for reduplication come from Princeton University’s WordNet. Full sources and licences.