introvert

introvert
/ˈɪntrəvɜ:t; `ɪntrəˌvət/ n
person who is more interested in his own thoughts and feelings than in things outside himself, and is often shy and unwilling to speak or join in activities with others （思想感情等）内向的人. Cf 参看 extrovert.

牛津英汉双解词典