back end vs extremity

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. 

extremity

noun
  • The most extreme or furthest point of something. 

  • A hand or foot. 

  • A limb (“major appendage of a human or animal such as an arm, leg, or wing”). 

  • An extreme measure. 

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