diffident vs self-conscious

diffident

adj
  • Lacking self-confidence; timid; modest 

self-conscious

adj
  • Uncomfortably over-conscious of one's appearance or behaviour; socially ill at ease. 

  • Excessively conscious of one's appearance or behaviour. 

  • Aware of oneself as an individual being. 

How often have the words diffident and self-conscious occurred in a corpus of books? (source: Google Ngram Viewer )