This is the 10873rd most frequent Portuguese word.
indignar
To provoke anger or outrage.
Here, "indignar" means to provoke intense anger or displeasure due to unfairness.
A injustiça social pode indignar muitas pessoas.
Social injustice can outrage many people.
In this context, "indignar-se" reflects personally experiencing a moment of anger due to an observed negative action.
Ela ficou indignada com o comportamento rude dele.
She became outraged by his rude behavior.
Here, "indignar-se" points to the act of guarding oneself against unnecessary anger due to trivial events.