Yeast, n.
(Synop., § 130), n. [A-S. gist, D. gist, gest, M. H. Ger. gest, jest, gis, N. H. Ger. gischt, gäscht, O. H. Ger. gesam, jesan, gerian, jērian, to ferment, M. H. Ger. gesen, jesen, geschen, gischen, geran, N. H. Ger. gischen, gäschen, gähren.] [Also yest.]
Sense 1. The foam or froth of beer or other liquor in fermentation; a preparation used for raising dough for bread or cakes, and making it light and puffy; barm; ferment.
Sense 2. Spume or foam of water. [Obs.] Shak.