Jaunty rhythm (4)
I believe the answer is:
lilt
'jaunty rhythm' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lilt that I've seen before include "Swing - music" , "Tune with light pleasant rhythm" , "Rising and falling of the voice in speech" , "Cadence (in speech)" , "Light graceful swinging rhythm" .)