above board vs hush-hush

above board

prep
  • Openly, without deceit. 

  • Honestly, reputably. 

hush-hush

adj
  • Secret, not spoken of (or spoken of only in hushed whispers between insiders). 

noun
  • secrecy; covert operation 

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