leaven

/ˈlɛvən/

/ˈlɛvɪn/

Other forms: leavened; leavening; leavens

Leaven, as a noun, is that which causes transformation. It’s the source of yeast that makes your bread rise, it’s the risen bread, and it’s anything that changes the nature of something else.

Coming through Old French from the Latin verb levare, which means “to raise,” leaven changes everything. It makes dough go from flat to loaf, and it’s also the term to describe the risen dough before it’s baked. And leaven can be anything that causes transformation — "Winning the lottery will be the leaven that allows you to travel the world." Additionally it’s a verb: "When you bake bread, you leaven the dough to make it rise."

Definitions of leaven

1. noun

   a substance used to produce fermentation in dough or a liquid
   synonyms: leavening

   types:

   baking powder

   any of various powdered mixtures used in baking as a substitute for yeast

   sourdough

   a leaven of dough in which fermentation is active; used by pioneers for making bread

   barm, yeast

   a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey

   yeast cake

   small cake of compressed moist yeast

   brewer's yeast

   yeast used in fermenting beer

   mother

   a stringy slimy substance consisting of yeast cells and bacteria; forms during fermentation and is added to cider or wine to produce vinegar

   type of:

   substance

   a particular kind or species of matter with uniform properties
2. noun

   an influence that works subtly to lighten or modify something
   synonyms: leavening

   type of:

   imponderable

   a factor whose effects cannot be accurately assessed
3. verb

   cause to puff up with a leaven
   synonyms: prove, raise

   type of:

   bring up, elevate, get up, lift, raise

   raise from a lower to a higher position