Past tense of buff; polished something to a smooth, shiny finish, or removed the skin/hair from something.
From 'buff', which originally referred to the soft leather made from buffalo hide, then generalized to mean polishing or smoothing anything to a buff-like finish.
Your car's 'buffed' finish comes from the same root as 'buffalo'—through buff leather. It's a beautiful linguistic chain: animal → leather made from it → the polishing process that creates it.
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