armoury vs citadel

armoury

noun
  • A collection of weapons and materiel. 

  • Heraldry 

  • A place where arms are kept, an arsenal. 

  • A place where arms are made. 

  • The manufacture of armour and arms; arming, armouring. 

citadel

noun
  • An armoured portion of a warship, housing important equipment. 

  • A stronghold or fortified place. 

  • A Salvation Army meeting place. 

  • A strong fortress that sits high above a city. 

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