dropped ceiling vs plafond

dropped ceiling

noun
  • A secondary ceiling, suspended from above, used to conceal wiring, plumbing and ducts 

plafond

noun
  • A ceiling, especially one that is ornately decorated. 

  • The tibial plafond. 

  • A painting or decoration on a ceiling. 

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