- leaven, leavening - an influence that works subtly to lighten or modify something; "his sermons benefited from a leavening of humor"
--1 is a kind of imponderable
- leaven, leavening - a substance used to produce fermentation in dough or a liquid
--2 is a kind of substance, matter
--2 has particulars: baking powder; sourdough; yeast, barm