introvert

v. turn inwards upon itself; focus on one's own thoughts and feelings (Psychology)

n. one who is inward looking, one who tends to focus on his own thoughts and feelings

The trait of Extraversion-Introversion is a central dimension of human personality. Extraverts (sometimes called "extroverts") are gregarious, assertive, and generally seek out excitement. Introverts, in contrast, are reserved, thoughtful, and self-reliant. They are not necessarily asocial, but they tend to have smaller circles of friends, and are less likely to thrive on making new social contacts.
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Introvert /in·tro·vert/ 1. a person whose interest is turned inward to the self. 2. to turn one's interest inward to the self. 3. [more]Introvert - Community and Resources

Noun
1. (psychology) a person who tends to shrink from social contacts and to become preoccupied with their own thoughts
(antonym) extrovert, extravert
(hypernym) person, individual, someone, somebody, mortal, human, soul
(classification) psychology, psychological science
Verb
1. fold inwards; "some organs can invaginate"
(synonym) invaginate
(hypernym) draw in, retract
(hyponym) intussuscept
(derivation) invagination, introversion
2. turn inside; "He introverted his feelings"
(hypernym) change, alter, modify

(v. t.)
To turn or bend inward.
  

(v. t.)
To look within; to introspect.