a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey
source: WordNet 3.0
any of various single-celled fungi that reproduce asexually by budding or division
source: WordNet 3.0
The foam, or troth (top yeast), or the sediment (bottom yeast), of beer or other in fermentation, which contains the yeast plant or its spores, and under certain conditions produces fermentation in saccharine or farinaceous substances; a preparation used for raising dough for bread or cakes, and making it light and puffy; barm; ferment.
