covert vs under-the-table

covert

adj

  • Under coverture. 

  • Secret, surreptitious, concealed. 

noun

  • A covering. 

  • A disguise. 

  • A feather that covers the bases of flight feathers. 

  • Area of thick undergrowth where animals hide. 

  • A hiding place. 

under-the-table

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