observe vs onlook

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). 

onlook

verb
  • To look on or look at; watch; observe; view; regard. 

noun
  • The act of looking on (something); observation. 

  • One's perspective or outlook. 

  • That which is looked at, regarded, or considered. 

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