Last order for sailor (4)
I believe the answer is:
salt
'sailor' is the definition.
(salt is a kind of sailor)
'last order' is the wordplay.
'order' is an anagram indicator.
'last' anagrammed gives 'SALT'.
'for' is the link.
(Other definitions for salt that I've seen before include "NaCl" , "Sea dog" , "Crystalline substance for the table" , "Seasoning; old sailor" , "A defence against ice" .)