egoism. egotism

In 2002, I asked Merriam-Webster the following question. Kory L. Stamper replied as follows.

Q: How do egotism and egoism differ?

A: “Egotism” is the earlier word, appearing about 60 years before “egoism” did, sometime around 1720. Initially, it simply referred to the overuse of the first person pronoun, and then to excessive talk about oneself. Around 1800, it gained the common “conceit” sense that we use today. “Egotism” has rarely been used in a scholarly or clinical sense.

“Egoism,” on the other hand, began in scholarly and philosophical circles. Arriving in English in the 1780s, it was used first for the idea that nothing apart from the speaker’s mind truly exists (this sense was often used to refer to the logic of one’s opponents, naturally). Within a few decades, it came to be used to refer to the ethical stance that one’s self-interests are the foundations for personal morality and action. Only in the 1840s was it made synonymous with “egotism,” no doubt because of the similarity in spelling and the implication that an egoist thinks very highly of himself and would have quite a sense of self-importance.