1º_ While it means "brother", it is also used as an expression to call a friend, companion or even a stranger as an affectionate way to address him. 2º_ Friar, religious, is the same use that is given in Spanish to "brother in the faith".
It is a word from the German language, meaning brother. Friend of extreme confidence, companion, confidant, carnal. It can also mean in the religious field brother of faith, friar or friar.