This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. An agent that causes rising, fermentation, or ferment; leaven.

adj. made light by aeration

n. a leavening agent

n. The act of making light, or causing to ferment, by means of leaven.

n. That which leavens or makes light.

n. The act of making light by means of leaven; the act of exciting fermentation in anything.

n. That which leavens or makes light.

n. a substance used to produce fermentation in dough or a liquid

n. an influence that works subtly to lighten or modify something

"The men were mostly Swiss, but with a leavening from the German states, and they were a sober, steady battalion that Wellesley planned to lead to the Inner Palace to protect its contents and its harem from the ravages of the attackers."

imponderable   

unleavened    leaven   

leaven