E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
in printing, is a black smear or blotch made by leaving too much ink on the part. Caxton set up his printing press in the scriptorium of Westminster Abbey; and the associations of this place gave rise to the slang expressions monk and friar for black and white defects. (See FRIAR, CHAPEL.)
Give a man a monk (French, Luy bailler le moyne). To do one a mischief. Rabelais says that Grangousier (after the battle of Picrochole) asked what was become of Friar John; to which Gargantua replied, No doubt the enemy has the monk, alluding to the pugnacious feats of this wonderful churchman, who knocked men down like ninepins. (Rabelais: Gargantua and Pantagruel, book i. 45.)