Definitions
1.NounAny agent used to make dough rise or to have a similar effect on baked goods.
2.NounAnything that induces change, especially a corrupting or vitiating change.
3.NounChametz.
4.VerbTo add a leavening agent."Yeast is used to leaven bread, making it rise during baking."
5.VerbTo cause to rise by fermentation.
6.VerbTo temper an action, decision, attitude, characteristic, etc.
7.VerbTo imbue; to infect; to vitiate."The comedian's jokes helped leaven the atmosphere during the serious meeting.; Her optimism seemed to leaven the otherwise tense environment."
8.VerbTo rise or become larger; to prove. (Can we add an example for this sense?)