introvert (v.) Look up introvert at Dictionary.com
1650s, from Latin intro "inward, within" (see intro-) + vertere "to turn" (see versus).
introvert (n.) Look up introvert at Dictionary.com
1883, in zoology, "part or organ which is turned in upon itself," from introvert (v.). The psychological sense "introverted person" (opposed to extrovert) is 1918, from German, introduced there by C.G. Jung (1875-1961).