plinth vs underfloor

plinth

noun
  • A base or pedestal beneath a cabinet. 

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

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

underfloor

noun
  • A layer of flooring beneath the main floor surface. 

adj
  • Located beneath the floor. 

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