half-boot vs moon boot

half-boot

noun
  • A boot with a short top covering only the ankle. 

moon boot

noun
  • A type of footwear made popular in the 1970s, with a thin rubber outsole and no distinct left or right feet. 

  • A large hard plastic covering, used to protect a broken foot or ankle while it heals. 

How often have the words half-boot and moon boot occurred in a corpus of books? (source: Google Ngram Viewer )