covert vs in petto

covert

adj
  • Secret, surreptitious, concealed. 

  • Under coverture. 

noun
  • A covering. 

  • A disguise. 

  • A feather that covers the bases of flight feathers. 

  • Area of thick undergrowth where animals hide. 

  • A hiding place. 

in petto

adj
  • Secret, private. 

  • Designated as a cardinal but not yet announced. 

adv
  • Privately, in secret. 

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