sadness has 5 distinct synonyms spread across 3 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. Its one recorded opposite is happiness.
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.
emotions experienced when not in a state of well-being
Synonyms, antonyms and the broader and narrower relations for sadness come from Princeton University’s WordNet. Full sources and licences.
the state of being sad
“she tired of his perpetual sadness”
the quality of excessive mournfulness and uncheerfulness