Lead-free petrol or paint has no lead in it. Lead here is the heavy grey metal, not the verb that sounds like “leed.” For many years petrol and some paints had lead in them because it made engines run smoothly and paint last; though actually it was bad for the brain, especially in children, so countries pushed lead-free petrol and lead-free paint. You will see the words on pumps and tins. It is a practical label, not slang. In this word, lead sounds like “led.”