negative has 7 distinct synonyms spread across 5 of its 12 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 3 recorded opposites are neutral, positive, affirmative.
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.
expressing or consisting of a negation or refusal or denial
not indicating the presence of microorganisms or disease or a specific condition
“the HIV test was negative”
reckoned in a direction opposite to that regarded as positive
“negative interest rates”
designed or tending to discredit, especially without positive or helpful suggestions
“negative criticism”
a reply of denial
“he answered in the negative”
a piece of photographic film showing an image with light and shade or colors reversed
2 of the 12 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for negative.
Synonyms, antonyms and the broader and narrower relations for negative come from Princeton University’s WordNet. Full sources and licences.