Furtive attention-getter (4)
I believe the answer is:
psst
'furtive attention-getter' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for psst that I've seen before include "attempt to attract attention" , "Sound used to attract someone's attention" , "Here's a secret" , "Sibilant whisper to attract attention" , "that attracts attention" .)