word forming element indicating "oneself," also "automatic," from Old English use of self (pron.) in compounds, such as selfbana "suicide," selflice "self-love, pride, vanity, egotism," selfwill "free will."
mid-15c., "significant, of much import, bearing weight or consequence," from Medieval Latin importantem (nominative importans) "important, momentous," present-participle adjective from importare "be significant in," from Latin importare "bring in, convey, bring in from abroad," from assimilated form of in- "into, in" (from PIE root *en "in") + portare "to carry," from PIE root *per- (2) "to lead, pass over." The meaning "pretentious, pompous" is from 1713. Related: Importantly. Compare import (v.) and (n.).
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<a href="https://www.etymonline.com/word/self-important">Etymology of self-important by etymonline</a>
Harper, D. (n.d.). Etymology of self-important. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/self-important