commentator vs glossarist

commentator

noun
  • A medieval legal scholar who authored prose commentaries on civil law; (specifically) a member of a comparatively innovative 14th-century school of jurisprudence, typically distinguished from the earlier glossators. 

  • A person who comments; especially someone who is paid to give his/her opinions in the media about current affairs, sports, etc. 

glossarist

noun
  • someone who writes a glossary 

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