covertly vs sidelong

covertly

adv
  • In a covert manner, secretly. 

sidelong

adj
  • Slanting or sloping; oblique. 

  • Indirect; suggestive; not straightforward. 

  • Directed to the side; sideways. 

  • Along the side of something. 

adv
  • obliquely 

  • Towards the side; sideways. 

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