subclass vs subfamily

subclass

noun
  • A secondary class within a main class. 

  • A rank directly below class. 

  • An object class derived from another class (its superclass) from which it inherits a base set of properties and methods. 

verb
  • To cause (an object) to act as an instance of a subclass (by creating the desired subclass and instantiating an object of this subclass). 

  • (in object-oriented programming) To create a subclass of (some class). 

subfamily

noun
  • A secondary or subordinate grouping. 

  • A taxonomic category ranking between a family and a genus; formerly called a tribe 

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