Comment by jtheory

Ha! You got not just one, but TWO careful completely disingenuous replies.

"Bro" is short for brother the same way that "gay" means "happy". Well, sure, that's trivially true, but it kind of matters what people actually mean when they use a word.

Of course you're right; I have a biological brother and we don't call each other "bro". Here's what google turns up: http://www.npr.org/blogs/codeswitch/2013/06/21/193881290/jea... ...though I'm sure a bit more searching will find more direct treatments out there of what "bro" means....