What is the X in X-mas?
1714, as a term in metaphysics, from Latin ego "I" (cognate with Old English ic, see I). Psychoanalytic sense is from 1894; sense of "conceit" is 1891. Ego trip first recorded 1969.
In the book of Egoism it is written, Possession without obligation to the object possessed approaches felicity. [George Meredith, "The Egoist," 1879]
ego e·go (ē'gō, ěg'ō)
In psychoanalytic theory, the division of the psyche that is conscious, most immediately controls thought and behavior, and mediates between the person and external reality.
The “I” or self of any person (ego is Latin for “I”). In psychological terms, the ego is the part of the psyche that experiences the outside world and reacts to it, coming between the primitive drives of the id and the demands of the social environment, represented by the superego.
Note: The term ego is often used to mean personal pride and self-absorption: “Losing at chess doesn't do much for my ego.”