Vehicle or its petrol store (4)
I believe the answer is:
tank
This could be a double definition.
'vehicle' is the first definition.
(I know that tank is a type of vehicle)
'petrol store' is the second definition.
'tank' can be an answer for 'store' (thesaurus). I'm not sure about the 'petrol' bit.
'or its' acts as a link.
Can you help me to learn more?
(Other definitions for tank that I've seen before include "Military vehicle (for fish?)" , "Container for fish (or soldiers?)" , "Cistern - armoured vehicle" , "Miltary vehicle" , "Septic container" .)