hold back vs retard

hold back

verb
  • To delay the progress of, especially in school. 

  • To act with reserve; to contain one's full measure or power. 

  • To contain; stop. 

retard

verb
  • To keep delaying; to continue to hinder; to prevent from progressing. 

  • To put off; to postpone. 

  • To decelerate; to slow down. 

noun
  • Retardation; delay. 

  • A slowing down of the tempo; a ritardando. 

  • A person or being who is extremely stupid or slow to learn. 

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