(n) a fictional work which portrays an elaborate account of a particular historical event or movement in a more or less believable way, but using fictitious source material.
A case can be made for Dan Brown's The Da Vinci Code being the central text of the Factasy genre; however, an equally compelling case can be made for the inclusion of such divergent works as Susanna Clarke's Jonathan Strange and Mr. Norrell
a fact that provokes fantasy or is fantastic by itself; a literary or artistic genre that combines complete facticity with unbridled fantasy.
The center of our galaxy tastes like raspberries and smells rum. This factasy is a recent discovery of astronomers.
I am writing a factasy based on recent calculations: each ejaculation contains about 15 terabytes of genetic information transferred at a speed of 5 terabytes per second.