pilot officer vs subaltern

pilot officer

noun
  • The lowest rank of a commissioned officer in the RAF, equivalent to an Army ensign or coronet 

subaltern

noun
  • A commissioned officer having a rank below that of captain; a lieutenant or second lieutenant. 

  • A subordinate. 

  • A subaltern proposition; a proposition implied by a universal proposition. 

  • A member of a group that is socially, politically and geographically outside of the hegemonic power structure of the colony and of the colonial homeland. 

adj
  • Asserting only a part of what is asserted in a related proposition. 

  • Of a lower rank or position; inferior or secondary; especially (military) ranking as a junior officer, below the rank of captain. 

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