"turn within, direct inward," 1650s, from Latin intro "inward, within" (see intro-) + vertere "to turn" (from PIE root *wer- (2) "to turn, bend").
1878, in zoology, "part or organ which is turned in upon itself," from introvert (v.). The psychological sense "introverted person" (opposed to extrovert) is 1917, from German, introduced there by C.G. Jung (1875-1961).
"outgoing, overtly expressive person," 1916, extravert (spelled with -o- after 1918, by influence of introvert), from German Extravert, from extra "outside" (see extra-) + Latin vertere "to turn" (from PIE root *wer- (2) "to turn, bend"). Used (with introvert) in English by doctors and scientists in various literal senses since 1600s, but popularized in a psychological sense early 20c. by Carl Jung. Related: Extroverted.