mu vs vacuity

mu

noun
  • Nothingness; nonexistence; the illusory nature of reality. 

  • The 12th letter of the Modern Greek alphabet. 

  • A unit of surface area, currently equivalent two-thirds of a decare (about 666 meters squared). 

intj
  • Neither yes nor no. 

vacuity

noun
  • Physical emptiness, an absence of matter; vacuum. 

  • Idleness; listlessness. 

  • Emptiness. 

  • An empty or inane remark or thing. 

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