egoism has 4 distinct synonyms spread across 1 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is altruism.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
(ethics) the theory that the pursuit of your own welfare in the basis of morality
concern for your own interests and welfare
Synonyms, antonyms and the broader and narrower relations for egoism come from Princeton University’s WordNet. Full sources and licences.