Noun
A boy; especially, a boy servant.
Any male servant; a menial.
A tricky, deceitful fellow; a dishonest person; a rogue; a villain.
A playing card marked with the figure of a servant or soldier; a jack.
Source: Webster's dictionaryNo man is so much a fool as not to have wit enough sometimes to be a knave; nor any so cunning a knave as not to have the weakness sometimes to play the fool. George Savile, 1st Marquess of Halifax
I am always afraid of a fool one cannot be sure he is not a knave. William Hazlitt
Titles are marks of honest men, and wise The fool or knave that wears a title lies. Edward Young
Everyone is glad to see a knave caught in his own trap. German Proverb
For an honest man half his wits are enough; the whole is too little for a knave. Italian Proverb
Never in speech with a foolish knave shouldst thou waste a single word. Norse Proverb