sidelong vs surreptitiously

sidelong

adv
  • obliquely 

  • Towards the side; sideways. 

adj
  • Slanting or sloping; oblique. 

  • Indirect; suggestive; not straightforward. 

  • Directed to the side; sideways. 

  • Along the side of something. 

surreptitiously

adv
  • In a surreptitious manner; stealthily, furtively, secretly. 

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