explain vs fetter

explain

verb
  • To make plain, manifest, or intelligible; to clear of obscurity; to illustrate the meaning of. 

  • To give a valid excuse for past behavior. 

  • To make something plain or intelligible. 

fetter

noun
  • A chain or similar object used to bind a person or animal – often by its legs (usually in plural). 

  • Anything that restricts or restrains. 

verb
  • To restrain or impede; to hamper. 

  • To shackle or bind up with fetters. 

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