family unit vs gens

family unit

noun
  • A unit of people consisting of family members, distant or immediate. 

gens

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

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

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