barm vs brewer's yeast

barm and brewer's yeast both are nouns.

Word	Noun	Adjective	Verb	Adverb
barm	Yes	No	No	No
brewer's yeast	Yes	No	No	No

As nouns, brewer's yeast is a hyponym of barm; that is, brewer's yeast is a word with a more specific, narrower meaning than barm:

barm: a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey
brewer's yeast: yeast used in fermenting beer

Other hyponyms of barm include yeast cake, mother.

barm (noun)	brewer's yeast (noun)
a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey	used as a leaven in baking and brewing
	yeast used in fermenting beer