surd vs waterproof

surd

adj
  • unvoiced; voiceless 

  • Involving surds, or irrational numbers; not capable of being expressed in rational numbers. 

noun
  • An irrational number, especially one expressed using the √ symbol. 

  • A voiceless consonant. 

waterproof

adj
  • Incapable of failing; unassailable. 

  • Resistant to the effects of water. 

  • Made of or covered with material that doesn't allow water in. 

noun
  • A substance or preparation for rendering cloth, leather, etc., impervious to water. 

  • Cloth made waterproof, or any article made of such cloth, or of other waterproof material, as rubber; especially, an outer garment made of such material. 

verb
  • To make waterproof or water-resistant. 

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