Source : Webster's Revised Unabridged Dictionary (1913)

Leaven \Leav"en\, v. t. [imp. & p. p. {Leavened}; p. pr. & vb.
   n. {Leavening}.]
   1. To make light by the action of leaven; to cause to
      ferment.

            A little leaven leaveneth the whole lump. --1 Cor.
                                                  v. 6.

   2. To imbue; to infect; to vitiate.

            With these and the like deceivable doctrines, he
            leavens also his prayer.              --Milton.

Source : WordNet®

leavened
     adj : made light by aerating, as with yeast or baking powder;
           often used as a combining form; "leavened bread";
           "well-leavened"; "yeast-leavened breads" [ant: {unleavened}]