buckram vs rigid

buckram

verb
  • To stiffen with or as if with buckram. 

noun
  • A coarse cloth of cotton, linen or hemp, stiffened with size or glue, used in bookbinding to cover and protect the books, in garments to keep them in the form intended, and for wrappers to cover merchandise. 

  • A plant, Allium ursinum, also called ramson, wild garlic, or bear garlic. 

rigid

adj
  • Stiff, rather than flexible. 

  • Fixed, rather than moving. 

  • Uncompromising. 

  • Rigorous and unbending. 

noun
  • An airship whose shape is maintained solely by an internal and/or external rigid structural framework, without using internal gas pressure to stiffen the vehicle (the lifting gas is at atmospheric pressure); typically also equipped with multiple redundant gasbags, unlike other types of airship. 

  • A bicycle with no suspension system. 

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