Salad dressing base (3)
I believe the answer is:
oil
'salad dressing base' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oil that I've seen before include "Lubricating liquid" , "Liquid fuel" , "Thick liquid that doesn't dissolve in water" , "Cooking agent" , "Viscous substance for lubrication" .)