grammar - What does "brother mine" mean?

What exactly does "brother mine" mean? Is it the same as "my brother"?

As far as I know "brother" is a noun and "mine" is a pronoun, so it doesn't make much sense to me why one can precede the other.

Answer

It means "my brother".

It's an archaic formation; once standard English, but now only used poetically, especially in a few stock phrases (of which "brother mine" is perhaps the most common).

Comparably, to use mine in this sense before the noun is also archaic and now only used poetically, especially in a few stock phrases, of which "mine host" is perhaps the most common.