dogmatism n.

"a settled opinion, a principle held as being firmly established," c. 1600 (in plural dogmata), from Latin dogma "philosophical tenet," from Greek dogma (genitive dogmatos) "opinion, tenet," literally "that which one thinks is true," from dokein "to seem good, think" (from PIE root *dek- "to take, accept"). Regarded in 17c.-18c. as a Greek word in English but subsequently nativized.

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.