Attention-getter at sea (4)
I believe the answer is:
ahoy
'attention-getter at sea' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ahoy that I've seen before include "Cry at sea" , "Temporarily blind" , "Nautical greeting" , "Mariner's call" , "Hello there on board!" .)