Lead-in to a secret (4)

I believe the answer is:

psst

(Other definitions for psst that I've seen before include "Call to attract attention" , "Interjection to draw attention" , "Hissing noise to attract attention" , "Whispered exclamation to attract attention" , "Noise used to attract someone's attention privately" .)

I've seen this clue in the Newsday.

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