A dishonest or unscrupulous man. The knave was caught trying to cheat the villagers out of their money.
A playing card bearing a representation of a soldier or servant, typically ranking below a queen and above a ten; a jack. He laid down the knave of hearts to win the trick.
Archaic: A male servant or a man of lowly birth; a boy. In the medieval chronicles, the young knave carried his master's armor.