covertness vs hush-hush

covertness

noun

  • The characteristic of being covert. 

hush-hush

noun

  • secrecy; covert operation 

adj

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

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