family unit vs maternal

family unit

noun

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

maternal

noun

  • A person related through the mother, or her side of the family; a maternal relative. 

adj

  • Derived from the mother as opposed to the foetus during pregnancy. 

  • Of or pertaining to a mother; having the characteristics of a mother; motherly. 

  • Related through the mother, or her side of the family. 

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