Main Entry: ¹yeast

Pronunciation: \ˈyēst, especially Southern & Midland ˈēst\

Function: noun

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

Date: before 12th century

1 a : a yellowish surface froth or sediment that occurs especially in saccharine liquids (as fruit juices) in which it promotes alcoholic fermentation, consists largely of cells of a fungus (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>