"Wanna hear a secret?" (4)
I believe the answer is:
psst
'wanna hear a secret?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for psst that I've seen before include "attempt to attract attention" , "Here's a secret" , "Sibilant sound to attract attention furtively" , "(Whispered) may I have your attention?" , "Whispered exclamation to attract attention" .)