leavening vs barm

leavening and barm both are nouns.

Word	Noun	Adjective	Verb	Adverb
leavening	Yes	No	No	No
barm	Yes	No	No	No

As nouns, barm is a hyponym of leavening; that is, barm is a word with a more specific, narrower meaning than leavening:

leavening: a substance used to produce fermentation in dough or a liquid
barm: a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey

Other hyponyms of leavening include baking powder, sourdough, yeast.

leavening (noun)	barm (noun)
an influence that works subtly to lighten or modify something	a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey
a substance used to produce fermentation in dough or a liquid