lean-to vs skillion

lean-to

noun
  • A shelter with a sloped roof; also a building with a similar construction attached to the side of a building as an extension. 

skillion

noun
  • A room built against the back of another building, having a separate roof. 

  • Any indefinitely large number. 

How often have the words lean-to and skillion occurred in a corpus of books? (source: Google Ngram Viewer )