soundless vs surd

soundless

adj
  • Without sound. 

  • Not capable of being sounded or fathomed. 

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. 

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