1785, in metaphysics, "the theory that a person has no proof that anything exists outside his own mind," from French égoisme (1755), from Modern Latin egoismus, from Latin ego (see ego). Meaning "doing or seeking of that which affords pleasure or advances interest" is from 1800; opposed to altruism, but not necessarily "selfish." Meaning "self-centeredness" is from 1840. Between egoism and egotism, egoism is more correctly formed; there formerly was a useful distinction, with egotism tending to take the senses "self-centeredness" and "extensive use of 'I'" and leaving to egoism the theoretical sense in metaphysics and ethics.
