Yeast (noun)

A type of fungus that is used in the process of fermentation in baking and brewing.

Origin:

Middle english yest, from old english gæst, from latin gistus, from greek zōstēs, from zōein to ferment, from zōos leaven.

Examples:

1. The bread dough needs yeast to rise.
2. He added yeast to the grape juice to make wine.
3. She made her own yeast to use in her bread recipe.
4. The beer brewing process requires yeast to ferment the sugars.
5. Yeast is used to ferment the dough and make it rise.