surd vs unclear

surd

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

  • unvoiced; voiceless 

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

  • A voiceless consonant. 

unclear

adj
  • Not clearly or explicitly defined. 

  • Not easy to see or read; indecipherable or unreadable. 

  • Ambiguous; liable to more than one interpretation. 

  • Not having a clear idea; uncertain. 

verb
  • To undo the process of clearing. 

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