postgraduate vs pregraduate

postgraduate

adj
  • Of studies which take place after having successfully completed a degree course. 

noun
  • A person continuing to study in a field after having successfully completed a degree course. 

pregraduate

adj
  • Of or pertaining to those studies that take place before a student completes a degree course. 

noun
  • A person who is taking an academic course but has not yet graduated. 

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