sidelong vs surreptitious

sidelong

adj
  • Indirect; suggestive; not straightforward. 

  • Slanting or sloping; oblique. 

  • Directed to the side; sideways. 

  • Along the side of something. 

adv
  • obliquely 

  • Towards the side; sideways. 

surreptitious

adj
  • Stealthy, furtive, well hidden, covert (especially movements). 

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