yeast

1 of 2

noun

ˈyēst 

 especially Southern and Midland US  ˈēst

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

yeast-like adjective

or less commonly yeastlike

ˈyēst-ˌlīk 

 especially Southern and Midland US  ˈēst-

yeast

2 of 2

verb

yeasted; yeasting; yeasts

intransitive verb

: ferment, froth

Synonyms

Noun

• incentive
• impetus
• encouragement
• stimulus
• motivation

Examples of yeast in a Sentence

Noun

taxation without representation proved to be the yeast of rebellion

Recent Examples on the Web

Noun

Whole cluster pressed and fermented with native yeast, this succulent rose brims with bright fresh strawberry and watermelon notes. —Katie Kelly Bell, Forbes.com, 26 June 2025

Motif FoodWorks, a company that was using yeast to produce a meaty-tasting protein called Hemami, went out of business the same year. —Elizabeth Kolbert, New Yorker, 23 June 2025

Verb

The mashing process converts starches into sugars, which yeast ferments into alcohol. —Joseph V Micallef, Forbes.com, 26 Apr. 2025

The grains are a mix of probiotic bacteria and yeast that ferment milk into kefir cheese. —Katie Hunt, CNN, 25 Sep. 2024

Word History

Etymology

Noun

Middle English yest, from Old English gist; akin to Old High German jesen, gesen to ferment, Greek zein to boil

First Known Use

Noun

before the 12th century, in the meaning defined at sense 1a

Verb

1819, in the meaning defined above

Phrases Containing yeast

• baker's yeast
• brewer's yeast
• nutritional yeast
• yeast infection

Rhymes for yeast

• deceased
• decreased
• increased
• northeast
• policed
• released
• southeast
• beast
• ceased
• creased
• east
• feast

Kids Definition

yeast

noun

ˈyēst,

ˈēst

1

a

: a one-celled fungus that produces alcohol during the process of fermentation

also : any of various similar fungi

b

: a yellowish foamy material that may occur on the surface of sweet liquids (as fruit juices) undergoing fermentation and that consists chiefly of yeast cells and carbon dioxide

c

: a commercial product containing living yeast cells that is used mostly in the making of alcoholic beverages and as a leaven especially in baking bread

2

: something that causes motion or activity

yeasty

ˈyē-stē

ˈē-stē

adjective

Medical Definition

yeast

noun

ˈyēst 

1

: 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

yeastlike

-ˌlīk 

adjective