Leaven/ˈlevn/ Definition 1 of 3Pro Tip 1/3Culinary Term Used mostly in cooking to describe ingredients that help dough rise. The recipe requires a teaspoon of leaven for the pastry. Pro Tip 2/3Literal Use 'Leaven' is usually used literally in the context of baking and not as a metaphor. His grandmother taught him how to add leaven to the mix. Pro Tip 3/3Physical Change Leaven causes a visible change, making the dough expand and become fluffy. Without leaven, the dough remained flat and hard.