E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A lad, a garcon, a servant. (Anglo-Saxon, cnáfa; German, knabe.) The knave of clubs, etc., is the son or servant of the king and queen thereof. In an old version of the Bible we read: Paul, a knave of Jesus Christ, called to be an apostle, etc. (Rom. i. 1).
This version, we are told, is in the Harleian Library, but is generally supposed to be a forgery. But, without doubt, Wycliff (Rev. xii. 5, 13) used the compound Knave-child, and Chaucer uses the same in the Man of Lawes Tale, line 5130.