Pirate, if at sea, has a drink before dinner (8)
I believe the answer is:
aperitif
'a drink before dinner' is the definition.
(I've seen this before)
'pirate if at sea' is the wordplay.
'at sea' is an anagram indicator.
'pirate'+'if'='pirateif'
'pirateif' anagrammed gives 'APERITIF'.
'has' is the link.
(Other definitions for aperitif that I've seen before include "alcohol before meal" , "Alcoholic drink to stimulate appetite" , "Alcoholic drink to whet the appetite" , "Pre-dinner drink" , "it's served before dinner" .)