Surprise run on Baltic oil (9)
I believe the answer is:
lubricant
'oil' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for lubricant that I've seen before include "it has a smoothing effect" , "E.g. oil" , "Eg, grease" , "Substance used to reduce friction" , "Oil or grease" .)