The abstract noun related to the adjective "brave" is bravery.

Here's why:

* Brave is an adjective that describes a quality of a person.

* Bravery is the noun that represents that quality itself.

Let's look at an example:

* "The soldier showed great bravery in the face of danger."

Here, "bravery" is the abstract noun representing the quality of being brave that the soldier possessed.