According to various sources at dictionary.com, the word "bribe" is Middle English, from the Old French, piece of bread given as alms. The shift of meaning to "gift given to influence corruptly" is first attested 1535. The original meaning of the word is said to be from the base bri(m)b- denoting something small.
(My apologies to Gov. Blagojevich for contributing to the burial of the principle of "innocent until proven guilty" in America. Talk about trial and conviction by public opinion...)