slur vs slur over

slur is a noun but slur over is not a noun.

Word	Noun	Adjective	Verb	Adverb
slur	Yes	No	Yes	No
slur over	No	No	Yes	No

slur (noun)	slur over (noun)
a blemish made by dirt
a disparaging remark
(music) a curved line spanning notes that are to be played legato

slur (verb)	slur over (verb)
become vague or indistinct	treat hurriedly or avoid dealing with properly
utter indistinctly
speak disparagingly of; e.g., make a racial slur
play smoothly or legato