flatiron vs ironstone

flatiron

noun
  • A pair of metal tongs with heated ceramic plates used for straightening hair. 

  • A steeply sloping triangular landform created by the differential erosion of a steeply dipping, erosion-resistant layer of rock overlying softer strata. 

  • a quadrilateral with two parallel sides, one of which is very short, and whose non-parallel sides are longer than either parallel side. 

  • A simple iron (for pressing laundry) which is heated on a stove. 

adj
  • Having a flatiron shape. 

ironstone

noun
  • A type of vitreous pottery similar to stoneware 

  • Any ore of iron which is impure through the admixture of silica or clay. 

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