yeast

leaven, unleavened

Definition:

"Leaven" is a general term for a substance that causes bread dough to expand and rise. "Yeast" is a specific kind of leaven.

In some English translations, the word for leaven is translated as "yeast," which is a modern leavening agent that fills the bread dough with gas bubbles, making the dough expand before baking it. The yeast is kneaded into the dough so that it spreads throughout the entire lump of dough.
In Old Testament times, the leavening or rising agent was produced by allowing the dough to sit for awhile. Small amounts of dough from a previous batch of dough were saved as leavening for the next batch.
When the Israelites escaped from Egypt, they didn't have time to wait for bread dough to rise, so they made bread without leaven to take with them on their journey. As a reminder of this, every year the Jewish people celebrate Passover by eating bread that has no leaven in it.

The ideas of "leaven" and "yeast" can also be used in figurative ways.

The terms "leaven" and "yeast" are used figuratively in the Bible as a picture of how sin spreads through a person's life or how sin can influence other people.
They can also refer to false teaching which can spread to many people and influences them.
They are also used in a positive way to explain how the influence of God's kingdom spreads from person to person.

This could be translated as "leaven" or "substance that causes dough to rise" or "expanding agent." The word "rise" could be expressed as "expand" or "get bigger" or "puff up."
If a local leavening agent is used for making bread dough rise, that term can be used. If the language has a well-known, general term that means, "leavening," this would be the best term to use.

leaven, leavened, leavens, unleavened, yeast