difference vs subspecies

difference

noun
  • The quality or attribute which is added to those of the genus to constitute a species; a differentia. 

  • The result of a subtraction; sometimes the absolute value of this result. 

  • A disagreement or argument. 

  • An addition to a coat of arms to distinguish two people's bearings which would otherwise be the same. See augmentation and cadency. 

  • A characteristic of something that makes it different from something else. 

  • The quality of being different. 

  • The set of elements that are in one set but not another ( scriptstyle A◌̅B). 

  • Significant change in or effect on a situation or state. 

  • A Boolean operation which is true when the two input variables are different but is otherwise false; the XOR operation ( scriptstyle A◌̅B+◌̅AB). 

subspecies

noun
  • A subdivision of a species in other scientific disciplines. 

  • A taxon at that rank, often indicated with trinomial nomenclature (such as Felis silvestris silvestris in zoology and Pinus nigra subsp. salzmannii in botany). 

  • A rank in the classification of organisms, below species. 

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