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yeast

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(yēst)

noun

any of various single-celled ascomycetous fungi in which little or no mycelium develops and which ordinarily reproduce by budding: they ferment sugars to form alcohol and carbon dioxide; esp.,
1. any of various yeasts (esp. genus Saccharomyces) used in food production, as in making beer, wine, etc. and as a leavening in baking
2. any of various yeasts (esp. genus Candida) causing infections or diseases
brewer's yeast
1. the yellowish, moist mass of yeast plants occurring as a froth on fermenting solutions
2. this substance dried in flakes or granules or compressed into cakes
foam; froth
1. something that agitates or causes ferment; leaven
2. ferment; agitation

Origin: ME yest < OE gist, akin to Ger gischt, spray, froth & OHG jesan, to ferment < IE base *yes-, to foam, boil up > Gr zein, to boil, seethe

intransitive verb

Rare to froth or ferment

See yeast in American Heritage Dictionary 4

noun

a. Any of various unicellular fungi of the genus Saccharomyces, especially S. cerevisiae, reproducing by budding and from ascospores and capable of fermenting carbohydrates.
b. Any of various similar fungi.
Froth consisting of yeast cells together with the carbon dioxide they produce in the process of fermentation, present in or added to fruit juices and other substances in the production of alcoholic beverages.
A powdered or compressed commercial preparation, having yeast cells and inert material such as meal and used chiefly as a leavening agent or as a dietary supplement.
Foam; froth.
An agent of ferment or activity: political agitators who are the yeast of revolution.