1
a
: a yellowish surface froth or sediment that occurs especially in saccharine liquids (such as fruit juices) in which it promotes alcoholic fermentation, consists largely of cells of a fungus (such as the saccharomyces, Saccharomyces cerevisiae), and is used especially in the making of alcoholic liquors and as a leaven in baking
b
: a commercial product containing yeast fungi in a moist or dry medium
c(1)
: a unicellular fungus that is present and functionally active in yeast, usually has little or no mycelium, and reproduces by budding
(2)
: any of various similar fungi
2
archaic
: the foam or spume of waves
3
: something that causes ferment or activity
were all seething with the yeast of revolt—
J. F. Dobie
J. F. DobieExamples of yeast in a Sentence
Noun
taxation without representation proved to be the yeast of rebellion
Recent Examples on the Web
Katie Parla, Saveur, 30 Oct. 2025
Probiotics are live bacteria and yeasts believed to have various health benefits, but different strains target different systems.
—Lucy Notarantonio, MSNBC Newsweek, 30 Oct. 2025
Erica Sloan, SELF, 7 July 2025
The mashing process converts starches into sugars, which yeast ferments into alcohol.
—Joseph V Micallef, Forbes.com, 26 Apr. 2025
See All Example Sentences for yeast
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Noun
Set aside until the yeast has dissolved, about 15 minutes.
—Katie Parla, Saveur, 30 Oct. 2025
Probiotics are live bacteria and yeasts believed to have various health benefits, but different strains target different systems.
—Lucy Notarantonio, MSNBC Newsweek, 30 Oct. 2025
Verb
Yes, there are a handful of studies, albeit small ones, that suggest probiotics may help clear or slash recurrence of BV and possibly yeast.
—Erica Sloan, SELF, 7 July 2025
The mashing process converts starches into sugars, which yeast ferments into alcohol.
—Joseph V Micallef, Forbes.com, 26 Apr. 2025
See All Example Sentences for yeast
Cite this Entry
“Yeast.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/yeast. Accessed 3 Nov. 2025.
Copy CitationMedical Definition
yeast
noun1
: a unicellular chiefly ascomycetous fungus (as of the family Saccharomycetaceae) that has usually little or no mycelium, that typically reproduces asexually by budding, and that includes forms (as Saccharomyces cerevisiae) which cause alcoholic fermentation and are used especially in the making of alcoholic beverages and leavened bread
2
: a yellowish surface froth or sediment that occurs especially in sugary fermenting liquids (as fruit juices) and consists chiefly of yeast cells and carbon dioxide
3
: a commercial product containing yeast cells in a moist or dry medium
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