substrate vs trackbed

substrate

noun
  • The substance lining the bottom edge of an enclosure. 

  • An underlying layer; a substratum. 

  • A surface on which an organism grows, or to which an organism or an item is attached. 

  • A language that is replaced in a population by another language and that influences the language imposed on its speakers. 

  • A surface to which a substance adheres. 

  • A metal which is plated with another metal which has different physical properties. 

  • A substance acted upon, as by an enzyme. 

adj
  • Having very slight furrows. 

trackbed

noun
  • The layer of gravel or other foundation on which a railway track is laid. 

  • The land on which a railway (especially one that has been closed or dismantled) was built; the roadbed for a railroad. 

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