self-interest vs egoism

self-interest and egoism both are nouns.

Word	Noun	Adjective	Verb	Adverb
self-interest	Yes	No	No	No
egoism	Yes	No	No	No

As nouns, self-interest and egoism are synonyms defined as:

Other synonyms of self-interest include egocentrism, self-centeredness, self-concern.

self-interest (noun)	egoism (noun)
concern for your own interests and welfare	concern for your own interests and welfare
taking advantage of opportunities without regard for the consequences for others	(ethics) the theory that the pursuit of your own welfare is the basis of morality