Is the booty as in shake your booty related to a pirate’s booty? The booty that means “derriere” is an alteration of botty, which is itself an alteration of bottom. The booty that means “loot” or “plunder”...
botty-bot n.—Gloss: the rear end or derrière. «If I’m going to wear pants, I’m going to wear something that actually contains my entire botty-bot—instead of just hanging around the middle area, scantily, supposedly sexily, like a gift...