faithless vs irreligious

faithless

adj
  • Not believing in God, religion, or a comparable ideology. 

  • Not true to allegiance, duty, or vows 

  • Lacking faith; lacking belief in something. 

  • Unfaithful (said of people, towards their partners) 

  • Serving to disappoint or deceive 

  • Not observant of promises or covenants. 

irreligious

adj
  • Contrary to religious beliefs and practices. 

  • In conscious rejection of religion. 

  • Having no relation to religion. 

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