legion vs regiment

legion

verb
  • To form into legions. 

noun
  • The major unit or division of the Roman army, usually comprising 3000 to 6000 infantry soldiers and 100 to 200 cavalry troops. 

  • A combined arms major military unit featuring cavalry, infantry, and artillery, including historical units such as the British Legion, and present-day units such as the Spanish Legion and the French Foreign Legion. 

  • A large military or semi-military unit trained for combat; any military force; an army, regiment; an armed, organized and assembled militia. 

  • A national organization or association of former servicemen, such as the American Legion. 

  • A large number of people; a multitude. 

  • A great number. 

adj
  • Numerous; vast; very great in number 

regiment

verb
  • To form soldiers into a regiment. 

  • To systematize, or put in rigid order. 

noun
  • A unit of armed troops under the command of an officer, and consisting of several smaller units; now specifically, usually composed of two or more battalions. 

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