positive has 14 distinct synonyms spread across 9 of its 13 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 2 recorded opposites are negative, neutral.
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.
indicating existence or presence of a suspected condition or pathogen
“a positive pregnancy test”
impossible to deny or disprove
“incontrovertible proof of the defendant's innocence”
reckoned, situated or tending in the direction which naturally or arbitrarily is taken to indicate increase or progress or onward motion
“positive increase in graduating students”
the primary form of an adjective or adverb; denotes a quality without qualification, comparison, or relation to increase or diminution
a film showing a photographic image whose tones correspond to those of the original subject
1 of the 13 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for positive.
Synonyms, antonyms and the broader and narrower relations for positive come from Princeton University’s WordNet. Full sources and licences.