[rodric]

Modern French has had little influence on English. As I understand it, the -our forms are evolutions from the Norman French spellings that introduced these Latinate words into English after the Conquest. In the Renaissance, as many words made their way into English directly from Latin, there was something of a desire to Latinize the spellings of these words to their original -or forms. This had some traction in Britain (eg, horror, tremor, governor) but really took root in America.