by-product vs outcome

by-product and outcome both are nouns.

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

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

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

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

by-product (noun)	outcome (noun)
a product made during the manufacture of something else	something that results
a secondary and sometimes unexpected consequence	a phenomenon that follows and is caused by some previous phenomenon