covenant vs undertake

covenant

verb
  • To bind oneself in contract. 

  • To enter into, or promise something by, a covenant. 

  • To enter a formal agreement. 

  • To make a stipulation. 

noun
  • A promise, incidental to a deed or contract, either express or implied. 

  • An incidental clause in an agreement. 

  • An agreement to do or not do a particular thing. 

  • A pact or binding agreement between two or more parties. 

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 covenant and undertake occurred in a corpus of books? (source: Google Ngram Viewer )