dichotomy vs trichotomy

dichotomy

noun
  • A separation or division into two; a distinction that results in such a division. 

  • The division of a genus into two species; a division into two subordinate parts. 

  • A phase of the moon when it appears half lit and half dark, as at the quadratures. 

  • Such a division involving apparently incompatible or opposite principles; a duality. 

  • The division of a class into two disjoint subclasses that are together comprehensive, as the division of man into white and not white. 

  • Division and subdivision; bifurcation, as of a stem of a plant or a vein of the body into two parts as it proceeds from its origin; often successive. 

trichotomy

noun
  • Division or separation into three groups or pieces. 

  • the property of an order relation whereby, given an ordered pair of elements (of a given algebraic structure), exactly one of these is true: the first element is 'less than' the second one, the second is 'less than' the first, or the two elements are equal. 

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