1911 Encyclopædia Britannica/Knave

KNAVE (O.E. cnafa, cognate with Ger. Knabe, boy), originally a male child, a boy (Chaucer, Canterbury Tales: “Clerk’s Tale,” I. 388). Like Lat. puer, the word was early used as a name for any boy or lad employed as a servant, and so of male servants in general (Chaucer: “Pardoner’s Tale,” 1. 204). The current use of the word for a man who is dishonest and crafty, a rogue, was however an early usage, and is found in Layamon (c. 1205). In playing-cards the lowest court card of each suit, the “jack,” representing a medieval servant, is called the “knave.” (See also Valet.)