petrol vs leaded petrol

petrol and leaded petrol both are nouns.

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

As nouns, leaded petrol is a hyponym of petrol; that is, leaded petrol is a word with a more specific, narrower meaning than petrol:

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
leaded petrol: gasoline treated with a lead compound to reduce motor knocks

Other hyponyms of petrol include leaded gasoline, napalm, unleaded gasoline, unleaded petrol.

petrol (noun)	leaded petrol (noun)
a volatile flammable mixture of hydrocarbons (hexane and heptane and octane etc.) derived from petroleum; used mainly as a fuel in internal-combustion engines	gasoline treated with a lead compound to reduce motor knocks