A lump of highly fermented dough put into breaddough to cause it to rise. Jesus used leaven to refer to something small or unnoticeable that slowly and steadily affected the whole. He compared the kingdom of God to leaven in its ability to transform the nature of the flour; and he compared the teaching of the Pharisees and Sadducees to leaven that corrupts religion with its characteristics of outward show, hypocrisy, and skepticism.