1. To play smoothly or legato; of musical passages.
2. To speak disparagingly of; e.g., make a racial slur
3. To utter indistinctly.

(Music) A curved line spanning notes that are to be played legato.
In musical notation, a curved line written above or below a group of notes, indicating that all the associated notes are to be played or sung legato (smoothly). If staccato dots appear beneath the slur, then this indicates portato, a form of detached articulation. A slur connecting two notes of the same pitch is called a tie.