n. 1 a greyish-yellow fungous substance obtained esp. from fermenting malt liquors and used as a fermenting agent, to raise bread, etc. 2 any of various unicellular fungi in which vegetative reproduction takes place by budding or fission. yeastless adj. yeastlike adj.
[ OE gist, giest (unrecorded): cf. MDu. ghist, MHG jist, ON jöstr ]