ceiling vs mansard roof

ceiling

noun
  • The highest altitude at which an aircraft can safely maintain flight. 

  • The overhead interior surface that covers the upper limits of a room. 

  • The smallest integer greater than or equal to a given number. 

  • The upper limit of an object or action. 

  • The measurement of visible distance from ground or sea level to an overcast cloud cover; under a clear sky, the ceiling measurement is identified as "unlimited." 

  • The overhead closure of a room. 

  • The inner planking of a vessel. 

  • The maximum permitted level in a financial transaction. 

mansard roof

noun
  • A steeper roof that terminates into a flat roof at its high point. 

  • A roof having two slopes on each side, the lower one having a steeper pitch than the upper; this increases the volume of the enclosed space. 

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