bladder vs hot-air balloon

bladder

noun
  • The inflatable bag inside various balls used in sports, such as footballs and rugby balls. 

  • A sealed plastic bag that contains wine and is usually packaged in a cask. 

  • A flexible sac that can expand and contract and that holds liquids or gases. 

  • Anything inflated, empty, or unsound. 

  • Specifically, the urinary bladder. 

  • A hollow, inflatable organ of a plant. 

verb
  • To swell out like a bladder with air; to inflate. 

  • To store or put up in bladders. 

hot-air balloon

noun
  • A balloon-shaped aircraft whose bag is inflated with hot air; it carries passengers and crew in a gondola slung underneath. 

How often have the words bladder and hot-air balloon occurred in a corpus of books? (source: Google Ngram Viewer )