assassination vs first-degree murder

assassination

noun
  • The murder of a person, especially for political reasons or for personal gain. 

first-degree murder

noun
  • An act that constitutes the crime of first-degree murder. 

  • The criminal offence of murder in a form considered by law to be the most serious; the precise distinction may vary by jurisdiction but typically involves premeditation, or the choice of victim or other circumstances being regarded as especially blameworthy. 

How often have the words assassination and first-degree murder occurred in a corpus of books? (source: Google Ngram Viewer )