delay vs retard

delay

verb
  • To put off until a later time; to defer. 

  • To retard; to stop, detain, or hinder, for a time. 

noun
  • A period of time before an event occurs; the act of delaying; procrastination; lingering inactivity. 

  • An audio effects unit that introduces a controlled delay. 

  • Synonym of promise (“object representing delayed result”) 

  • An amount of time provided on each move before one's clock starts to tick; a less common time control than increment. 

retard

verb
  • To put off; to postpone. 

  • To decelerate; to slow down. 

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

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 delay and retard occurred in a corpus of books? (source: Google Ngram Viewer )