PIE word *bʰréh₂tēr Clipping of brother originating in African-American Vernacular English. Predates, but perhaps influenced, other slang clippings spelled with -h. This is a phonetic clipping: /ˈbɹʌðɚ/ → /bɹʌ/. Contrast bro, which is a clipping of the spelling of brother rather than the pronunciation.