noun

1. 1. a small piece of fermenting dough put aside to be used for producing fermentation in a fresh batch of dough
   2. leavening (sense )
2. leavening (sense )

Etymology: ME levein < OFr levain < VL *levamen (in L, alleviation) < L levare, to make light, relieve, raise: see lever

transitive verb

1. to make (batter or dough) rise before or during baking by means of a leavening agent
2. to spread through, causing a gradual change