I think the word brother (sometimes spelled brotha or bro) has been used for a long time among African Americans when talking to one another with the meaning of "pal" and not in a family context.
From the novels I read and the series I watch I have the feeling that for some years (difficult to date) the word is used more and more frequently by non-African Americans.
I've always gathered it was OK for African Americans to use the word when talking to one another.
To fully understand the feelings between the characters in the fiction I read or watch I'd like to know:
- what effect is conveyed when non-African Americans use it when talking to one another,
- if African Americans would call a non-African American brother,
- how African Americans would react if called brother by a non-African American, and
- how non-African Americans would react if called brother by an African American.
Best Answer
First of all, there are other meanings for the word brother outside the family context
The etymonline states that: "As a familiar term of address from one man to another, it is attested from 1912 in U.S. slang; the specific use among African Americans is recorded from 1973."
So, you should be aware that even if you are speaking specifically of the meaning of the word in subcultural context of African Americans, the word itself still carries the sense of kinsman, fellow member or simply someone who is related by common interest or ties.
Now, regarding who should use it for whom: another piece of the puzzle is that the term brotha is Jamaican English; which though it should not be confused with Rasta movement, often is (do notice that the context is not race anymore).
Now you have at least two subcultural contexts (race, religion), however for the true appreciation of applicability you should consider still more contexts, for example use in gang slang or in urban slang. Illustration of various contexts can be seen on urban dictionary for the term brotha.
For your questions:
All in all, the use of the word must be justified in some sense of it. Take note, when you say that you 'gathered that it was OK for African Americans to use the word when talking to one another' - that this is a statement that is a bit too general. Is it ok for every person in London to call each other 'old chump'? Is it appropriate? The answer is that it depends on the social connection that is shared and the context.
Similar situation is with word brother and the variations of it bro and brotha.