family unit vs succession

family unit

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

succession

noun
  • A race or series of descendants. 

  • In Roman and Scots law, the taking of property by one person in place of another. 

  • An act of following in sequence. 

  • A group of rocks or strata that succeed one another in chronological order. 

  • A right to take possession. 

  • A sequence of things in order. 

  • A passing of royal powers. 

  • Rotation, as of crops. 

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