be above-board vs come clean

be above-board

come clean

verb
  • 1921, B. M. Bower, chapter 6, in Sawtooth Ranch 

  • To confess; admit the truth. 

  • 1977 Oct. 23, John Gardner, "The World Of Tolkien," New York Times (retrieved 12 Sept 2013) 

  • 2005 August 8, "Quotes of the Day," Time (retrieved 12 Sept 2013) 

How often have the words be above-board and come clean occurred in a corpus of books? (source: Google Ngram Viewer )