Root meaning: The individual self, as distinct from other selves or the world. Ego is Latin for “I,” and when you say “I” you are referring to a self distinct from others.
ACIM: The entire self you think you are, the “I” you think you are. This self is false, was made by you, and is actually only a belief: The belief that you are a separate entity—a separate mind living within a separate body—that you have your own personal history and future, your own will and private thoughts, that you create yourself and sustain yourself. This is not who you are (see Christ and Son of God) and so the ego is a contradiction, an insane belief (see insanity), a mistaken identity. The ego is in direct, fundamental and total opposition to God (see devil). Its basic mood is fear of God, fear that it will disappear into His Love and Oneness. Its single motivation is to protect its “existence” from the “threat” of God and make itself a permanent, eternal reality. Its goal is to conquer and kill God and replace Him on His throne (see authority problem). To do this it must keep your eternal allegiance (as its maker) while at the same time trying to kill you, since you are God’s Son. It hopes to attain this paradoxical goal through persuading you to constantly attack. By promising you that attack will bring you pleasure and safety it keeps your allegiance. Yet it knows that attack will really bring death, since attack makes you think you deserve to die for your sins. The ego, however, is merely an idea, and thus has had no effect on who you really are. It has no power over you and can be relinquished whenever you choose, at which time it will simply disappear, be reinterpreted. See separation. See T-4.II, W-pII.12, C-2.