slur has 9 distinct synonyms spread across 3 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.
play smoothly or legato
“the pianist slurred the most beautiful passage in the sonata”
speak disparagingly of; e.g., make a racial slur
“your comments are slurring your co-workers”
become vague or indistinct
“The distinction between the two theories blurred”
(music) a curved line spanning notes that are to be played legato
a disparaging remark
“in the 19th century any reference to female sexuality was considered a vile aspersion”
Synonyms, antonyms and the broader and narrower relations for slur come from Princeton University’s WordNet. Full sources and licences.