redundancy has 1 distinct synonym spread across 1 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 messages to reduce the probability of errors in transmission
the attribute of being superfluous and unneeded
“the use of industrial robots created redundancy among workers”
(electronics) a system design that duplicates components to provide alternatives in case one component fails
Synonyms, antonyms and the broader and narrower relations for redundancy come from Princeton University’s WordNet. Full sources and licences.