What is the term for using a word in its own definition?

The term for using a word in its own definition is called circular definition.

It's a type of definition that uses the word being defined itself, leading to a logical fallacy. This is because it doesn't actually explain the meaning of the word but simply restates it in a different way.

For example:

* "Brave" means to be courageous. This doesn't tell us what "brave" means, as it simply replaces it with another word that is synonymous.

Circular definitions are considered uninformative and unsatisfactory as they do not provide a clear explanation of the word's meaning.