"Hey there!" (4)
'hey there' 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 "Hissing noise to attract attention" , "Sibilant whisper to attract attention" , "Here's a secret" , "Don't tell anyone" , "Noise used to attract someone's attention privately" .)
(Other definitions for hiya that I've seen before include "modern form of salve?" , "Hello!" , "Informal 19 across" , "Informal greeting" .)
(Other definitions for you that I've seen before include "The solver" , "Reader" , "who never can tell" , "Second person pronoun" , "whoever's reading this" .)