"Yo, over here!" (4)
I believe the answer is:
psst
'yo over here' 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 "Pay attention" , "Sound to call quietly" , "Call to attract attention" , "Quiet call for attention" , "Quiet attention-seeker" .)