unresponsiveness has 1 distinct synonym spread across 1 of its 1 sense. 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. Its one recorded opposite is responsiveness.
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.
the quality of being unresponsive; not reacting; as a quality of people, it is marked by a failure to respond quickly or with emotion to people or events
“she began to recover from her numb unresponsiveness after the accident”
Synonyms, antonyms and the broader and narrower relations for unresponsiveness come from Princeton University’s WordNet. Full sources and licences.