positivity has 8 distinct synonyms spread across 5 of its 5 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 negativity.
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 character of the positive electric pole
a quality or state characterized by certainty or acceptance or affirmation and dogmatic assertiveness
the quality of being encouraging or promising of a successful outcome
the quality of being undeniable and not worth arguing about
Synonyms, antonyms and the broader and narrower relations for positivity come from Princeton University’s WordNet. Full sources and licences.