courter vs girlfriend

courter

noun
  • One who courts; one who plays the lover, or solicits in marriage. 

girlfriend

noun
  • A term of address for a female friend or among gay men. 

  • A female partner in an unmarried romantic relationship. 

  • A fellow gay man, especially a friend as opposed to a sexual partner. 

  • A female friend. 

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