encumber vs undertake

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. 

undertake

verb
  • To commit oneself (to an obligation, activity etc.). 

  • To pass a slower moving vehicle on the curbside rather than on the side closest to oncoming traffic. 

  • To take upon oneself; to start, to embark on (a specific task etc.). 

noun
  • The passing of slower traffic on the curbside rather than on the side closest to oncoming traffic. 

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