counselor vs invigilator

counselor

noun
  • A children’s supervisor, usually at camp. 

  • A school counselor, often in a specialty such as careers, education, or health. 

  • A professional who counsels people, especially on personal problems. 

  • An attorney. 

  • A high ranking diplomat, usually just below an ambassador or minister. 

invigilator

noun
  • A person who supervises students during an examination; a proctor 

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