contribute vs encumber

contribute

verb
  • To give something that is or becomes part of a larger whole. 

encumber

verb
  • To burden with a legal claim or other obligation. 

  • To load down something with a burden. 

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

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