dripstone vs penthouse

dripstone

noun
  • A protective moulding over a door or window that allows rain to drip away from the structure. 

  • Stalactites and stalagmites collectively. 

  • A water filter in which impurities are removed by running water through a porous stone. 

penthouse

noun
  • An outhouse or other structure (especially one with a sloping roof) attached to the outside wall of a building, sometimes as protection from the weather. 

  • Any of the sloping roofs at the side of a real tennis court. 

  • An apartment or suite found on an upper floor, or floors, of a tall building, especially one that is expensive or luxurious with panoramic views. Sometimes these are located just under "penthouse mechanical" floors. 

verb
  • To provide with a penthouse, shelter by means of a shed sloping from a wall, or anything similar. 

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