"You shall not bob us out of our ____: if you do, our melancholy upon your head!” (Troilus and Cressida) (6)
I believe the answer is:
melody
(Other definitions for melody that I've seen before include "Harmonious tune or song" , "Air, tune" , "Agreeable succession of musical sounds" , "Refrain" , "It forms the core of a tune" .)