knag vs rail spike

knag

noun
  • A peg or hook for hanging something on 

  • A pointed rock or crag 

  • A small cask or barrel; a keg or noggin 

  • A knot in a piece of wood or the base of a branch 

  • A short spur or stiff projection from the trunk or branch of a tree, such as the stunted dead branch of a fir 

verb
  • To hang something on a peg 

rail spike

noun
  • A type of large nail with an offset head used to fasten a rail or base plate to a wooden railroad tie/sleeper. 

How often have the words knag and rail spike occurred in a corpus of books? (source: Google Ngram Viewer )