gens vs tribus

gens

noun
  • A tribal subgroup whose members are characterized by having the same descent, usually along the male line. 

  • A legally defined unit of Roman society, being a collection of people related through a common ancestor by birth, marriage or adoption, possibly over many generations, and sharing the same nomen gentilicium. 

  • A host-specific lineage of a brood parasite species.^([W]) 

tribus

noun
  • Synonym of tribe 

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