Greenhorn vs Pioneer

Greenhorn

name

  • A census-designated place in Plumas County, California, United States. 

Pioneer

name

  • A census-designated place in Amador County, California, United States. 

noun

  • A person born on/before 31 Dec 1949 and possessing Singapore citizenship on/before 31 Dec 1986, given this status and certain benefits to recognise their contributions to Singapore's early development. 

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