back end vs postern

back end

noun
  • The rear, back, or unseen portion (of something). 

  • The processing of spent fuel from a nuclear reactor into reusable materials. 

  • That part of a hardware or software system that is farthest from the user; the internals rather than the user interface. 

  • The latter end of any given time, especially the latter part of the year; autumn; late autumn. 

  • Money paid on a contingent deferred basis, for example, as a proportion of the profits or revenue of a work. 

postern

noun
  • A back gate, back door, side entrance, or other gateway distinct from the main entrance. 

  • A subterranean passage communicating between the parade and the main ditch, or between the ditches and the interior of the outworks. 

adj
  • Situated at the rear; posterior. 

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