double-cross vs frankness

double-cross

verb
  • To cross twice in hybridization, as (A × B) × (C × D); for example, in commercial hybrid seed corn, A through D are classically inbreds, and their grandoffspring is the seed for sale. 

  • To betray or go back on. 

frankness

noun
  • The state of being frank; candour; honesty. 

How often have the words double-cross and frankness occurred in a corpus of books? (source: Google Ngram Viewer )