Leaven

[lev-uh n] /ˈlɛv ən/

noun
1.
a substance, as yeast or baking powder, that causes fermentation and expansion of dough or batter.
2.
fermented dough reserved for producing fermentation in a new batch of dough.
3.
an element that produces an altering or transforming influence.
verb (used with object)
4.
to add leaven to (dough or batter) and cause to rise.
5.
to permeate with an altering or transforming element.
/ˈlɛvən/
noun
1.
any substance that produces fermentation in dough or batter, such as yeast, and causes it to rise
2.
a piece of such a substance kept to ferment a new batch of dough
3.
an agency or influence that produces a gradual change
verb (transitive)
4.
to cause fermentation in (dough or batter)
5.
to pervade, causing a gradual change, esp with some moderating or enlivening influence
n.

mid-14c., from Old French levain “leaven, sourdough” (12c.), from Latin levamen “alleviation, mitigation,” but used in Vulgar Latin in its literal sense of “a means of lifting, something that raises,” from levare “to raise” (see lever). Figurative use from late 14c.
v.

c.1400, from leaven (n.). Related: Leavened; leavening.

(1.) Heb. seor (Ex. 12:15, 19; 13:7; Lev. 2:11), the remnant of dough from the preceding baking which had fermented and become acid. (2.) Heb. hamets, properly “ferment.” In Num. 6:3, “vinegar of wine” is more correctly “fermented wine.” In Ex. 13:7, the proper rendering would be, “Unfermented things [Heb. matstsoth] shall be consumed during the seven days; and there shall not be seen with thee fermented things [hamets], and there shall not be seen with thee leavened mass [seor] in all thy borders.” The chemical definition of ferment or yeast is “a substance in a state of putrefaction, the atoms of which are in a continual motion.” The use of leaven was strictly forbidden in all offerings made to the Lord by fire (Lev. 2:11; 7:12; 8:2; Num. 6:15). Its secretly penetrating and diffusive power is referred to in 1 Cor. 5:6. In this respect it is used to illustrate the growth of the kingdom of heaven both in the individual heart and in the world (Matt. 13:33). It is a figure also of corruptness and of perverseness of heart and life (Matt. 16:6, 11; Mark 8:15; 1 Cor. 5:7, 8).