South Pacific boat (4)
'south pacific boat' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for proa that I've seen before include "Malay sailing-boat" , "Canoe-like boat of South Pacific" , "Malay sailing boat with outrigger" , "Vessel" , "Malay boat with identical ends and one outrigger" .)
(Another definition for prau that I've seen is " sailing vessel".)