middle school vs university

middle school

noun
  • An educational level or stage between primary school and secondary school. 

  • A school which crosses the traditional divide between primary school and secondary school. 

university

noun
  • Institution of higher education (typically accepting students from the age of about 17 or 18, depending on country, but in some exceptional cases able to take younger students) where subjects are studied and researched in depth and degrees are offered. 

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