eight-oar vs figure of eight

eight-oar

noun
  • Synonym of eight (“narrow rowing boat with eight rowers”) 

figure of eight

noun
  • The shape or form of an 8 (eight). 

  • A type of knot. 

  • A device for abseiling, so-called for its shape. 

How often have the words eight-oar and figure of eight occurred in a corpus of books? (source: Google Ngram Viewer )