by-product vs consequence

by-product and consequence both are nouns.

Word	Noun	Adjective	Verb	Adverb
by-product	Yes	No	No	No
consequence	Yes	No	No	No

As nouns, consequence is a hypernym of by-product; that is, consequence is a word with a broader meaning than by-product:

by-product: a secondary and sometimes unexpected consequence
consequence: a phenomenon that follows and is caused by some previous phenomenon

Other hypernyms of by-product include effect, event, issue, outcome, result, upshot.

by-product (noun)	consequence (noun)
a product made during the manufacture of something else	having important effects or influence
a secondary and sometimes unexpected consequence	the outcome of an event especially as relative to an individual
	a phenomenon that follows and is caused by some previous phenomenon