What is the difference between metaphysics and ontology?

Question

I know that ontology is a sub-field of metaphysics. But I can't see the difference between them. I mean ontology is defined as "The study of being and existence", and metaphysics is defined as "fundamental nature of being and the world"; is there a difference between these two definitions?

Answer 1

"I know that ontology is a sub-field of metaphysics."

It is? That's news to me. In my view, there is no difference between metaphysics and ontology.