Look here's ship entering port empty (4)
I believe the answer is:
psst
'look here's' is the definition.
Both the definition and answer are interjections.
Perhaps you can see an association between them that I can't see?
'ship entering port empty' is the wordplay.
'ship' becomes 'ss'.
'entering' is an insertion indicator.
'empty' says to hollow out the word (remove centre letters).
'port' with its centre taken out is 'pt'.
'ss' put within 'pt' is 'PSST'.
Can you help me to learn more?
(Other definitions for psst that I've seen before include "Sound to call quietly" , "Whispered attention grabber" , "Quiet call for attention" , "Listen!" , "Interjection to attract someone's attention without alerting others" .)