duffel bag vs duffle bag

duffel bag

noun
  • A large, cylindrical, duffel cloth bag used to carry personal gear, especially by soldiers. 

  • A smaller, cylindrical, cloth bag fashionable in the 1950s and 1960s. 

duffle bag

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