flatbread vs sourdough

flatbread

noun
  • A thin, flat bread, often made from unleavened dough. 

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 flatbread and sourdough occurred in a corpus of books? (source: Google Ngram Viewer )