betroth vs undertake

betroth

verb
  • To promise to take (as a future spouse); to plight one's troth to. 

  • To promise to give in marriage. 

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