surd vs voiceless

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. 

voiceless

adj
  • Lacking a voice, without vocal sound. 

  • Spoken without vibration of the vocal cords; unvoiced, surd, breathed. Examples: [t], [s], [f], [m̥], [u̥]. 

  • Without a vote; having no input into a decision. 

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