Spoke indistinctly with sounds running together, or made a mark connecting musical notes; also means treated disrespectfully.
Possibly from Dutch 'sluren' or related to 'slur' in the sense of 'drag.' The musical meaning developed separately in notation.
Speech slurring happens because your brain processes words faster than your mouth can physically articulate them—it's not laziness but a timing problem between brain speed and motor control.
Complete word intelligence in one call. Free tier — 50 lookups/day.