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.