observe vs spy

observe

verb
  • To notice or view, especially carefully or with attention to detail. 

  • To take note of and celebrate (a holiday or similar occurrence); to follow (a type of time or calendar reckoning). 

  • To comment on something; to make an observation. 

  • To follow or obey the custom, practice, or rules (especially of a religion). 

spy

verb
  • To spot; to catch sight of. 

  • To act as a spy. 

  • To search narrowly; to scrutinize. 

  • To explore; to see; to view; inspect and examine secretly, as a country. 

noun
  • A defensive player assigned to cover an offensive backfield player man-to-man when they are expected to engage in a running play, but the offensive player does not run with the ball immediately. 

  • A person who secretly watches and examines the actions of other individuals or organizations and gathers information on them (usually to gain an advantage). 

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