unleaded petrol vs petrol

unleaded petrol and petrol both are nouns.

Word	Noun	Adjective	Verb	Adverb
unleaded petrol	Yes	No	No	No
petrol	Yes	No	No	No

As nouns, petrol is a hypernym of unleaded petrol; that is, petrol is a word with a broader meaning than unleaded petrol:

unleaded petrol: gasoline that has not been treated with a lead compound
petrol: a volatile flammable mixture of hydrocarbons (hexane and heptane and octane etc.) derived from petroleum; used mainly as a fuel in internal-combustion engines

Other hypernyms of unleaded petrol include gas, gasolene, gasoline.

unleaded petrol (noun)	petrol (noun)
gasoline that has not been treated with a lead compound	a volatile flammable mixture of hydrocarbons (hexane and heptane and octane etc.) derived from petroleum; used mainly as a fuel in internal-combustion engines