air force vs contingent

air force

noun
  • A unit in the U.S. Air Force larger than a division but smaller than a command. 

  • A branch of the military mainly devoted to air warfare, as opposed to (land) army and navy. 

contingent

noun
  • A quota of troops. 

  • That which falls to one in a division or apportionment among a number; a suitable share. 

  • An event which may or may not happen; that which is unforeseen, undetermined, or dependent on something future. 

adj
  • Possible or liable, but not certain to occur. 

  • Dependent on something that is undetermined or unknown, that may or may not occur. 

  • Not logically necessarily true or false. 

  • Temporary. 

How often have the words air force and contingent occurred in a corpus of books? (source: Google Ngram Viewer )