introversion vs ruminating

introversion

noun
  • The action of turning one's thoughts upon internal or spiritual matters. 

  • Arrangement of two similar words, lines, etc. to form the middle part of a structure. 

  • A turning inward 

  • A personality orientation towards the self and mental abstraction; behavior expressing such orientation. 

ruminating

noun
  • An act of pondering over, meditation, or reflection. 

How often have the words introversion and ruminating occurred in a corpus of books? (source: Google Ngram Viewer )