A lot vs. Alot: 9 Grammatical Pitfalls
1781, "directed inward," past participle adjective from introvert. Psychological sense is from 1915.
introvert in·tro·vert (ĭn'trə-vûrt', ĭn'trə-vûrt')
v. in·tro·vert·ed, in·tro·vert·ing, in·tro·verts
To turn or direct inward.
To concentrate one's interests upon oneself.
To turn a tubular organ or part inward upon itself.
One whose thoughts and feelings are directed toward oneself.
An anatomical structure that is capable of being introverted.