ego:  Ego is Latin for ‘I’ (and comes in fact from the same Indo-European base as produced English I). English originally acquired it in the early 19th century as a philosophical term for the ‘conscious self’, and the more familiar modern uses – ‘self-esteem’, or more derogatorily ‘selfimportance’, and the psychologist’s term (taken up by Freud) for the ‘conscious self’ – date from the end of the century.
Derivatives include egoism , borrowed from French égoïsme, and egotism , perhaps deliberately coined with the t to distinguish it from egoism. And the acquisitions do not end there: alter ego, literally ‘other I, second self’, was borrowed in the 16th century, and the Freudian term superego, ‘beyond I’, entered the language in the 1920s. => i
1714, as a term in metaphysics, "the self; that which feels, acts, or thinks," from Latin ego "I" (cognate with Old English ic; see I). Psychoanalytic (Freudian) sense is from 1894; sense of "conceit" is 1891. Ego-trip first recorded 1969, from trip (n.). Related: egoical; egoity.
In the book of Egoism it is written, Possession without obligation to the object possessed approaches felicity. [George Meredith, "The Egoist," 1879]