quality has 11 distinct synonyms spread across 4 of its 7 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 essential and distinguishing attribute of something or someone
“the quality of mercy is not strained”
a degree or grade of excellence or worth
“the quality of students has risen”
high social status
“a man of quality”
1 of the 7 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 quality.
Synonyms, antonyms and the broader and narrower relations for quality come from Princeton University’s WordNet. Full sources and licences.