adjutant vs sub-lieutenant

adjutant

noun
  • A lower-ranking officer who assists a higher-ranking officer with administrative affairs. 

  • Any bird of the genus Leptoptilos, a branch of the stork family (Ciconiidae) native to India and Southeast Asia. 

  • An assistant. 

adj
  • Assistant; who helps a higher-ranking officer. 

sub-lieutenant

noun
  • A commissioned officer of the navy ranking above an acting sub-lieutenant and below a lieutenant. 

  • A commissioned officer of the Royal Navy ranking above a midshipman and below a lieutenant. 

How often have the words adjutant and sub-lieutenant occurred in a corpus of books? (source: Google Ngram Viewer )