Etymology
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ego (n.)

by 1707, in metaphysics, "the self; that which feels, acts, or thinks," from Latin ego "I" (cognate with Old English ic; see I); its use is implied in egoity.

They that have pleaded against Propriety, and would have all things common in this World, have forgotten that there is a Propriety, in our present Egoity, and Natural Constitution, which rendereth some accidental Propriety necessary to us (etc.) ["The Practical Works of the Late Reverend and Pious Mr. Richard Baxter," London, 1707]

Psychoanalytic (Freudian) sense is from 1894; sense of "conceit" is 1891. Ego-trip first recorded 1969, from trip (n.). Related: egoical.

In the book of Egoism it is written, Possession without obligation to the object possessed approaches felicity. [George Meredith, "The Egoist," 1879]
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alter ego (n.)
"second self, counterpart," 1530s, from Latin phrase (used by Cicero), "a second self, a trusted friend" (compare Greek allos ego); see alter and ego.
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super-ego (n.)
also superego, "that part of the psyche which controls the impulses of the id," 1924, as a translation of German über-Ich; see super- and ego.
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egocentric (adj.)
1890, from ego + -centric. Related: Egocentricity; egocentrism.
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egotize (v.)
"talk overmuch of oneself," 1775, from ego + -ize.
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egotheism (n.)
"deification of the self," 1855, from ego + -theism. Related: Egotheist (1849); egotheistic.
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egotist (n.)
1714, "one who makes too frequent use of the first-person singular pronoun," see ego + -ist. First attested in Joseph Addison (see egotism). Related: Egotistic; egotistical; egotistically.
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egoist (n.)
1763, in metaphysics, "one who maintains there is no evidence of the existence of anything but the self" (taking ego in a sense of "thinking subject"), from French égoiste (1755); see ego + -ist. Meaning "selfish person" is from 1879. Related: Egoistic; egoistical.
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egotism (n.)
1714, "too frequent use of 'I'," from ego + -ism. First used by Joseph Addison, who credits the term to "Port-Royalists" who used it in reference to obtrusive use of first person singular pronoun in writing, hence "talking too much about oneself." Meaning "self-conceit, selfishness" is from 1800. The -t- is abnormal, perhaps by influence of dogmatism.
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egoism (n.)
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.
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