retard vs shackle

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. 

shackle

verb
  • To render immobile or incapable; to inhibit the progress or abilities of. 

  • To shake, rattle. 

  • To restrain using shackles; to place in shackles. 

noun
  • A link for connecting railroad cars; a drawlink or draglink. 

  • A restraint on one's action, activity, or progress. 

  • A length of cable or chain equal to 12+¹⁄₂ fathoms or 75 feet, or later to 15 fathoms. 

  • A U-shaped piece of metal secured with a pin or bolt across the opening, or a hinged metal loop secured with a quick-release locking pin mechanism. 

  • A fetter-like band worn as an ornament. 

  • A restraint fit over a human or animal appendage, such as a wrist, ankle or finger; normally used in pairs joined by a chain. 

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