yeast
UK: jiːst | US: jiːst
n. a microscopic fungus used in fermentation (e.g., in baking or brewing)
n. a frothy or foamy substance formed during fermentation
n. (figuratively) an agent of change or excitement
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The word "yeast" traces back to Old English gist or gyst, meaning "foam" or "ferment," derived from Proto-Germanic jestuz. Its core idea of bubbling/fermentation persists in modern usage. The spelling evolved under influence of Middle Dutch gheest and Old High German jesan (to ferment). Unlike many scientific terms, "yeast" retains its ancient Germanic roots without clear morpheme divisions.
Bakers add yeast to dough to make bread rise.
The brewery uses a special strain of yeast for their beer.
A layer of yeast formed on the surface of the fermenting juice.
Her enthusiasm acted like yeast, energizing the whole team.
Ancient Egyptians utilized yeast long before its microbial nature was understood.