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