leavening

Noun

leav=en=ing

WORDNET DICTIONARY

leavening(n = noun.cognition) leaven - an influence that works subtly to lighten or modify something; "his sermons benefited from a leavening of humor"

is a kind of imponderable

leavening(n = noun.substance) leaven - a substance used to produce fermentation in dough or a liquid;

is a kind of substance

has particulars: baking powder, sourdough, barm, yeast

leavening, n.

The act of making light, or causing to ferment, by means of leaven. [1913 Webster]
That which leavens or makes light. Bacon. [1913 Webster]