extremity vs perimeter

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. 

perimeter

noun
  • The outer limits of an area. See synonyms at circumference. 

  • An instrument for determining the extent and shape of the field of vision. 

  • The length of such a boundary. 

  • The sum of the distance of all the lengths of the sides of an object. 

  • A fortified strip or boundary usually protecting a military position. 

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