In music, a curved line indicating that a melody is to be played legato or as a single phrase (4)
I believe the answer is:
slur
(Other definitions for slur that I've seen before include "Insinuation; indistinct utterance" , "Aspersion - speak indistinctly" , "Slight lack of distinction in speech" , "Contentious allegation" , "Speak disparagingly of - speak indistinctly" .)