genitor vs single parent

genitor

noun

  • a biological parent (either male or female), or the direct cause of an offspring. 

  • a generator; an originator 

single parent

noun

  • A parent who is the only guardian of offspring. 

verb

  • To act as the only guardian of offspring. 

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