flapjack vs sourdough

flapjack

noun
  • A bar made of (though not limited to) rolled oats, butter, golden syrup, and brown sugar, baked in a tray. 

  • A pancake. 

sourdough

noun
  • A type of bread dough leavened with yeast and lactobacilli that produce acids giving a sour taste. 

  • A 49er, a California Gold Rush miner. 

  • An old-timer, especially in Alaska. 

  • A permanent resident of the territory. Someone who has lived in the Yukon during all four seasons. 

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