Synonyms for Slur (same or very similar meaning)
WordNet sense 1 (a disparaging remark):
aspersion
WordNet sense 2 (a blemish made by dirt):
blot, daub, smear, smirch, smudge, spot
WordNet sense 3 (become vague or indistinct):
blur, dim
From the ODE community, based on WordNet
add/edit