dripstone vs mansard

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. 

mansard

noun
  • The upper storey of a building, surrounded by such a roof 

  • A mansard roof 

adj
  • having two slopes on each side, the lower being steeper than the upper 

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