plinth vs trackbed

plinth

noun
  • The bottom course of stones or bricks supporting a wall. 

  • A base or pedestal beneath a cabinet. 

  • A block or slab upon which a column, pedestal, statue or other structure is based. 

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 plinth and trackbed occurred in a corpus of books? (source: Google Ngram Viewer )