A tittering laugh (3-3)
I believe the answer is:
tee-hee
'a tittering laugh' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tee-hee that I've seen before include "Derisive giggle" , "laughing sound" , "Sound of a titter" , "Titter, giggle" , "A tittering laugh" .)