Condiment for Jack Tar (4)
I believe the answer is:
salt
This clue is a triple definition!
'condiment' is the first definition.
(I've seen this in another clue)
'for jack' is the second definition.
(thesaurus)
'tar' is the third definition.
(synonyms)
(Other definitions for salt that I've seen before include "Common substance" , "Seasoning; old sailor" , "Preservative" , "Condiment - old sailor" , "Condiment - experienced sailor" .)