[leav.en] n [ME levain, fr. MF, fr. (assumed) VL levamen, fr. L levare to raise--more at lever] (14c) 1 a: a substance (as yeast) used to produce fermentation in dough or a liquid; esp: sourdough b: a material (as baking powder) used to produce a gas that lightens dough or batter
2: something that modifies or lightens
[2]leaven vt leav.ened ; leav.en.ing (15c) 1: to raise (as bread) with a leaven
2: to mingle or permeate with some modifying, alleviating, or vivifying element syn see infuse