Bubba

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mid 19th century: alteration of brother.

wiktionary

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Possibly an alteration of brother or bub, said by a young child not yet able to pronounce brother properly, but note similar terms in other Germanic languages derived from Proto-Germanic *bō-, *bō-, such as West Frisian bobbe, German Bube(“boy”), dialectal Swedish babbe(“little boy”), English babe, Dutch boef(“mischievous lad, rascal”), Middle Low German bōve, and Icelandic bófi. Also compare sissy.

etymonline

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bubba (n.)

familiar address or nickname for a male, 1873 (in a South Carolina context), Southern U.S. slang, said to be a corruption of brother.