If your brother says he’s going to become a guerrilla, don't worry, he's not planning to become a hairy animal. Guerrilla fighters band together in a small underground army, usually trying to overcome a larger and more organized force.
Guerrilla and gorilla are pronounced the same — which makes it easy to remember how to say guerrilla — but they have different meanings. In Spanish, guerra means "war," and guerrilla means “little army.” Guerrilla fighters tend to work in small groups and use ambush and sabotage to surprise stronger, more traditional forces. You’ve might have heard of Che Guevara, a famous guerrilla fighter who was involved in the Cuban Revolution.