Jeer when greeting ship (4)
I believe the answer is:
hiss
'jeer' is the definition.
(I've seen this before)
'greeting ship' is the wordplay.
'greeting' becomes 'hi' (hi is a kind of greeting).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'hi'+'ss'='HISS'
'when' acts as a link.
(Other definitions for hiss that I've seen before include "Boo" , "Catcall" , "Sibilant sound made through the teeth" , "S-sound of disapproval" , "(Make noise to) express disapproval" .)