explain vs unfold

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. 

unfold

verb
  • To open (anything covered or closed); to lay open to view or contemplation; to bring out in all the details, or by successive development. 

  • To undo a folding. 

  • To release from a fold or pen. 

  • To turn out; to happen; to develop. 

  • To reveal. 

noun
  • In functional programming, a kind of higher-order function that is the opposite of a fold. 

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