The phrase to curry Fauvel developed meaning to ingratiate yourself with someone hoping for a favor in return, like you would by currying the rascally horse. At the time that the phrase developed in English, the poem was well known to educated people in Britain. As time went by the poem, and therefore the original meaning of Fauvel, was forgotten, and the word favour was substituted. While the word favour made perfect sense with the meaning of the phrase, the verb curry remained as a curious puzzle.By the way, the word for the spice curry came a few centuries later from Tamil via Portuguese.
Source: POSH and other language myths by Michael Quinion, 2004, Penguin Books, London
