ego vs self-importance

ego and self-importance both are nouns.

Word	Noun	Adjective	Verb	Adverb
ego	Yes	No	No	No
self-importance	Yes	No	No	No

As nouns, ego and self-importance are synonyms defined as:

ego and self-importance: an inflated feeling of pride in your superiority to others

Other synonyms of ego include egotism.

ego (noun)	self-importance (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