Favourite part, without ending fuel (6)
I believe the answer is:
petrol
'fuel' is the definition.
(I know that petrol is a type of fuel)
'favourite part without ending' is the wordplay.
I cannot quite understand how this works, but
'favourite' could be 'pet' (synonyms) and 'pet' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for petrol that I've seen before include "Common motor fuel" , "The juice" , "Fuel for the internal combustion engine" , "Common car fuel" , "Gasoline" .)