introvert (n.)

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).

introvert (v.)

1650s, from Latin intro "inward, within" (see intro-) + vertere "to turn" (from PIE root *wer- (2) "to turn, bend").