fulfill vs observe

fulfill

verb
  • To obey, follow, comply with (a rule, requirement etc.). 

  • To emotionally or artistically satisfy; to develop one's gifts to the fullest. 

  • To package, distribute, or ship goods. 

  • To satisfy, carry out, bring to completion (an obligation, a requirement, etc.). 

observe

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

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

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

  • To comment on something; to make an observation. 

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