surd vs tongueless

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. 

tongueless

adj
  • Expressed without speech; wordless, unspoken. 

  • Having no tongue. 

  • Making no sound; silent, speechless. 

  • Lacking speech; mute. 

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