subfamily vs subspecies

subfamily

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

  • A secondary or subordinate grouping. 

subspecies

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

  • 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 subdivision of a species in other scientific disciplines. 

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