ego vs egotism

ego and egotism both are nouns.

Word	Noun	Adjective	Verb	Adverb
ego	Yes	No	No	No
egotism	Yes	No	No	No

As nouns, ego and egotism are synonyms defined as:

ego and egotism: an inflated feeling of pride in your superiority to others

Other synonyms of ego include self-importance.

ego (noun)	egotism (noun)
(psychoanalysis) the conscious mind	an exaggerated opinion of your own importance
your consciousness of your own identity	an inflated feeling of pride in your superiority to others
an inflated feeling of pride in your superiority to others