retard vs slow

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. 

slow

verb
  • To keep from going quickly; to hinder the progress of. 

  • To become slow; to slacken in speed; to decelerate. 

  • To make (something) run, move, etc. less quickly; to reduce the speed of. 

adj
  • Behind in time; indicating a time earlier than the true time. 

  • Lacking spirit; deficient in liveliness or briskness. 

  • Not happening in a short time; spread over a comparatively long time. 

  • Of reduced intellectual capacity; not quick to comprehend. 

  • Not busy; lacking activity. 

  • Taking a long time to move or go a short distance, or to perform an action; not quick in motion; proceeding at a low speed. 

  • Not hasty; not tending to hurry; acting with deliberation or caution. 

noun
  • A slow song. 

  • Someone who is slow; a sluggard. 

adv
  • Slowly. 

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