obstruct vs retard

obstruct

verb
  • To impede, retard, or interfere with; hinder. 

  • To get in the way of so as to hide from sight. 

  • To block or fill (a passage) with obstacles or an obstacle. See synonyms at block. 

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