baking powder vs leavening

baking powder and leavening both are nouns.

Word	Noun	Adjective	Verb	Adverb
baking powder	Yes	No	No	No
leavening	Yes	No	No	No

As nouns, leavening is a hypernym of baking powder; that is, leavening is a word with a broader meaning than baking powder:

baking powder: any of various powdered mixtures used in baking as a substitute for yeast
leavening: a substance used to produce fermentation in dough or a liquid

Other hypernyms of baking powder include leaven.

baking powder (noun)	leavening (noun)
any of various powdered mixtures used in baking as a substitute for yeast	an influence that works subtly to lighten or modify something
	a substance used to produce fermentation in dough or a liquid