When something closely relates to a subject it is called the subject?

That's not quite right. When something closely relates to a subject, it's called related or relevant to the subject.

Here's why:

* Subject: The main topic or theme being discussed.

* Related: Having a connection or association to the subject.

* Relevant: Having a significant or important connection to the subject, directly contributing to understanding it.

For example, let's say the subject is "cats":

* Related: Dogs, kittens, animal care, feline behavior - all have a connection to cats, even if they aren't directly *about* cats.

* Relevant: Cat breeds, cat health, cat training - these topics directly relate to the understanding of cats.

So, while things related to a subject are closely associated, they aren't the subject itself.