What's the "een" in Halloween?
1650s, of thought or contemplation, from Modern Latin introversionem, noun of action from past participle stem of *introvertere (see introvert). Meaning "tendency to withdraw from the world" is from 1912.
introversion in·tro·ver·sion (ĭn'trə-vûr'zhən, -shən)
The act or process of introverting or the condition of being introverted.
The direction of or tendency to direct one's thoughts and feelings toward oneself.