Sound akin to a tap on the shoulder (4)

I believe the answer is:

psst

(Other definitions for psst that I've seen before include "Don't tell anyone" , "Quiet attention-seeker" , "Sibilant sound to attract attention furtively" , "Notice me" , "Interjection to attract someone's attention without alerting others" .)

I've seen this clue in the Universal.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.