What does the word leaven mean?

Usage examples for leaven

  1. The leaven of Christian morality was present in the lump of traditional social conditions; but it had not yet begun to work extensively. – Women of Early Christianity Woman: In all ages and in all countries, Vol. 3 (of 10) by Alfred Brittain Mitchell Carroll
  2. Here, however, within the bodies of animals and vegetables we find equivocal generation a necessity; nor do I see any way out of it except by maintaining that nothing is ever either quite dead or quite alive, but that a little leaven of the one is always left in the other. – The Note-Books of Samuel Butler by Samuel Butler
  3. The religion of Christ is a leaven of action, understanding, sacrifice, and charity. – Saint Augustin by Louis Bertrand