encumber vs restrict

encumber

verb
  • To restrict or block something with a hindrance or impediment. 

  • To burden with a legal claim or other obligation. 

  • To load down something with a burden. 

restrict

verb
  • To restrain within boundaries; to limit; to confine 

  • To consider (a function) as defined on a subset of its original domain. 

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