militia vs regiment

militia

noun
  • An army of trained civilians, which may be an official reserve army, called upon in time of need, the entire able-bodied population of a state which may also be called upon, or a private force not under government control. 

  • Synonym of militsia: the national police force of certain countries (e.g. Belarus). 

regiment

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. 

verb
  • To systematize, or put in rigid order. 

  • To form soldiers into a regiment. 

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