Major vs senior captain

Major

noun
  • Title for an army officer with the rank of major. 

name
  • A village in Saskatchewan, Canada. 

  • A surname. 

  • An unincorporated community in Kentucky. 

senior captain

noun
  • a military rank for a field officer above that of captain and below that of major 

  • a military rank for a naval officer above that of captain and below the admiral ranks or flag ranks 

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