What does overweening mean, in Don Quixote by Miguel de Cervantes?

Overweening means arrogant or excessively proud; exaggerated or excessive. In this passage from Don Quixote, a clergyman lectures Don Quixote for being a delusional knight. The clergyman tells him to go home, mind his own business, and stop making a fool of himself. In reply, Don Quixote says:
Knight I am, and knight I will die, if such be the pleasure of the Most High. Some take the broad road of overweening ambition; others that of mean and servile flattery; others that of deceitful hypocrisy, and some that of true religion; but I, led by my star, follow the narrow path of knight-errantry . . .