Definition of leavens:
(n) :
Any agent used to make dough rise or to have a similar effect on baked goods.
(v) :
(transitive) To cause to rise by fermentation.
(v) :
(transitive) To add a leavening agent.
(n) :
(figurative) Anything that induces change, especially a corrupting or vitiating change.
(v) :
(transitive, figuratively) To temper an action, decision, attitude, characteristic, etc.
(v) :
(transitive, figuratively) To imbue; to infect; to vitiate.