The act of making light, or causing to ferment, by means of leaven.

Any agent that causes a dough or batter to rise. Common leaveners include baking powder, baking soda and yeast. Natural leaveners are air (when beaten into eggs) and steam (in popovers and cream puffs).

An agent that produces gas in dough or batter by fermentation, raising and lightening it. Yeast, baking powder and baking soda are all common forms.

That which leavens or makes light.