Crossword Genius

Hey, lieutenant, crook petrol! (5)

Ross

I believe the answer is:

ethyl

I'm a little stuck... Click here to teach me more about this clue!

'petrol' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for ethyl that I've seen before include "-- Alcohol; -- acetate" , "Alkyl radical, base of common alcohol" , "C2H5" , "compound" .)

I've seen this clue in the Sydney Morning Herald.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.