aide-de-camp vs first lieutenant

aide-de-camp

noun
  • A military officer who serves as an adjutant to a higher-ranking officer, prince or other high political dignitary. 

first lieutenant

noun
  • An equivalent rank in other military forces. 

  • The second lowest rank of a commissioned officer in the United States Army, Air Force, or Marine Corps, ranking above a second lieutenant and below a captain. The rank of first lieutenant is equivalent to the naval rank of lieutenant junior grade. 

How often have the words aide-de-camp and first lieutenant occurred in a corpus of books? (source: Google Ngram Viewer )