arcanum vs hush-hush

arcanum

noun

  • A mystery or deep secret. 

  • An elixir or secret remedy. 

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 arcanum and hush-hush occurred in a corpus of books? (source: Google Ngram Viewer )