Slur comes from Middle English sloor ('thin mud'), related to Low German slurren ('to drag the feet'); the sense developed from 'to smear' to 'to disparage' and 'to pronounce indistinctly'. The historical chain includes Middle English sloor. The quoted older senses, "thin mud", "to drag the feet", "to smear", "to disparage", and "to pronounce indistinctly", supply the semantic anchors for slur. The formation is best read as borrowed: the word slur carries its older form-history into a compact English lexical shape. In present English it is used as a noun, "an insulting remark, or to pronounce words indistinctly". The result is a noun and verb whose etymology preserves both the older form and the later English specialization.