fixture has 12 distinct synonyms spread across 3 of its 4 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
an object firmly fixed in place (especially in a household)
the quality of being fixed in place as by some firm attachment
the act of putting something in working order again
Synonyms, antonyms and the broader and narrower relations for fixture come from Princeton University’s WordNet. Full sources and licences.