Last order for a sailor (4)
I believe the answer is:
salt
'a sailor' is the definition.
(salt is a kind of sailor)
'last order' is the wordplay.
'order' indicates an anagram.
'last' with letters rearranged gives 'SALT'.
'for' is the link.
(Other definitions for salt that I've seen before include "Brackish" , "Liveliness" , "Seasoning; old sailor" , "Condiment - experienced sailor" , "NaCl" .)