introvert

An introverted person: one who is considered more thoughtful than social, with a personality more inwardly than outwardly directed; one who often prefers to have time in non-social situations.

A reserved person.

An organ or other body part that is or can be turned inside out, especially an anterior portion of some annelid worms capable of retraction.

To turn inwards.

To think about internal or spiritual matters.

To withdraw an organ or body part within itself or its base.