fen vs lowland

fen

noun
  • A type of wetland fed by ground water and runoff, containing peat below the waterline, characteristically alkaline. 

  • A unit of currency in China, one-hundredth of a yuan. 

lowland

noun
  • An area which is considered particularly low or lower than surrounding areas. 

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