stairway vs step ladder

stairway

noun
  • A set of steps, with or without a case, that allow one to walk up or down. 

step ladder

noun
  • A ladder with steps or treads instead of rungs that is hinged in the middle to form an inverted V, with stays to keep the two halves at a fixed angle. 

  • The player over whom another player marks to take a spectacular mark. 

How often have the words stairway and step ladder occurred in a corpus of books? (source: Google Ngram Viewer )