The Collaborative International Dictionary of English v.0.48:

Introvert \In`tro*vert"\, v. t. [imp. & p. p. Introverted; p.
   pr. & vb. n. Introverting.] [Pref. intro- + L. vertere,
   versum, to turn.]
   [1913 Webster]
   1. To turn or bend inward. "Introverted toes." --Cowper.
      [1913 Webster]

   2. To look within; to introspect. --Lew Wallace.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Introvert \In"tro*vert`\, n.
   1. A person who is introverted; one concerned predominantly
      with himself or his own feelings. Contrasted with
      extrovert.
      [PJC]

   2. A person who is shy.
      [PJC]

   3. (Zool.) A part that can be introverted[1].
      [PJC]

WordNet (r) 3.0 (2006):

introvert
    n 1: (psychology) a person who tends to shrink from social
         contacts and to become preoccupied with their own thoughts
         [ant: extravert, extrovert]
    v 1: fold inwards; "some organs can invaginate" [syn:
         invaginate, introvert]
    2: turn inside; "He introverted his feelings"