Meaning

noun a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey

originFrom Middle English berme, berm, from Old English beorma, from Proto-West Germanic *bermō (“yeast; barm”); related to the dialectal Low German Bärm (“yeast”), from Middle Low German barm, berm. The cake sense is possibly a shortened form of barmcake, which would be made with yeast as described in that sense, or possibly it is from the Irish bairín breac, a type of bread.

Etymology from Wiktionary, CC BY-SA 3.0