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[yeest] /yist/
any of various small, single-celled fungi of the phylum Ascomycota that reproduce by fission or budding, the daughter cells often remaining attached, and that are capable of fermenting carbohydrates into alcohol and carbon dioxide.
any of several yeasts of the genus Saccharomyces, used in brewing alcoholic beverages, as a leaven in baking breads, and in pharmacology as a source of vitamins and proteins.
spume; foam.
ferment; agitation.
something that causes ferment or agitation.
verb (used without object)
to ferment.
to be covered with froth.
Origin of yeast
before 1000; Middle English ye(e)st (noun), Old English gist, gyst; cognate with Dutch gist, German Gischt yeast, foam, Old Norse jastr yeast, Greek zestós boiled, Sanskrit yásati (it) boils
Related forms
yeastless, adjective
yeastlike, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for yeast


any of various single-celled ascomycetous fungi of the genus Saccharomyces and related genera, which reproduce by budding and are able to ferment sugars: a rich source of vitamins of the B complex
any yeastlike fungus, esp of the genus Candida, which can cause thrush in areas infected with it
a commercial preparation containing yeast cells and inert material such as meal, used in raising dough for bread or for fermenting beer, whisky, etc See also brewer's yeast
a preparation containing yeast cells, used to treat diseases caused by vitamin B deficiency
froth or foam, esp on beer
(intransitive) to froth or foam
Derived Forms
yeastless, adjective
yeastlike, adjective
Word Origin
Old English giest; related to Old Norse jostr, Old High German jesan, Swedish esa, Norwegian asa, Sanskrit yasati
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for yeast

Old English gist "yeast," common West Germanic (cf. Middle High German gest, German Gischt "foam, froth," Old High German jesan, German gären "to ferment"), from PIE *jes- "boil, foam, froth" (cf. Sanskrit yasyati "boils, seethes," Greek zein "to boil," Welsh ias "seething, foaming").

Online Etymology Dictionary, © 2010 Douglas Harper
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yeast in Medicine

yeast (yēst)

  1. Any of various unicellular fungi of the genus Saccharomyces, especially S. cerevisiae, reproducing by budding and from ascospores and capable of fermenting carbohydrates.

  2. Any of various similar fungi.

  3. A commercial preparation in either powdered or compressed form containing yeast cells and inert material and used especially as a leavening agent or as a dietary supplement.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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yeast in Science
Any of various one-celled fungi that reproduce by budding and can cause the fermentation of carbohydrates, producing carbon dioxide and ethanol. There are some 600 known species of yeast, though they do not form a natural phylogenic group. Most yeasts are ascomycetes, but there are also yeast species among the basidiomycetes and zygomycetes. The budding processes in yeasts show a wide range of variations. In many yeasts, for example, the buds break away as diploid cells. Other yeasts reproduce asexually only after meiosis, and their haploid buds act as gametes that can combine to form a diploid cell, which functions as an ascus and undergoes meiosis to produce haploid spores. Still other yeasts form buds in both haploid and diploid phases. The ascomycete yeast Saccharomyces cerevisiae is used in baking to produce the carbon dioxide that leavens dough and batter. It has been the subject of extensive research in cell biology, and its genome was the first to be sequenced among eukaryotes. A variety of yeasts of the genus Saccharomyces are used in making beer and wine to provide alcohol content and flavor. Certain other yeasts, such as Candida albicans, are pathogenic in humans.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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