Modern term for a piece of music where a different text is set to the notes from that originally intended; e.g. an English text might be set to an originally Latin motet. An example would be the recasting of the lines (originally in Latin) 'Now at the beginning of the day/ to God as suppliants we pray' as the following, 'Now at the dawning of the day/ We must start drinking straight away'. Later, when friars began their mission to travel and preach to people outside the church, they used popular tunes, changing the words to suit their purposes. This use of music known to the general populace was why St Francis called his followers joculatores Dei, God's minstrels. [< Lat. contrafacio = to imitate, to counterfeit]
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.