Sailor’s last order (4)
I believe the answer is:
salt
'sailor's' is the definition.
(salt is a kind of sailor)
'last order' is the wordplay.
'order' indicates an anagram.
'last' anagrammed gives 'SALT'.
(Other definitions for salt that I've seen before include "NaCl" , "Pile up" , "Common substance" , "Crystalline substance used to season food" , "Condiment - experienced sailor" .)