baking powder vs leaven

baking powder and leaven both are nouns.

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

As nouns, leaven is a hypernym of baking powder; that is, leaven 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
leaven: a substance used to produce fermentation in dough or a liquid

Other hypernyms of baking powder include leavening.

baking powder (noun)	leaven (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

baking powder (verb)	leaven (verb)
	cause to puff up with a leaven