objective has 8 distinct synonyms spread across 4 of its 6 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 subjective.
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.
undistorted by emotion or personal bias; based on observable phenomena
“an objective appraisal”
serving as or indicating the object of a verb or of certain prepositions and used for certain other purposes
“objective case”
the lens or system of lenses in a telescope or microscope that is nearest the object being viewed
2 of the 6 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 objective.
Synonyms, antonyms and the broader and narrower relations for objective come from Princeton University’s WordNet. Full sources and licences.