refusal vs undertaking

refusal

noun
  • The act of refusing. 

  • Depth or point at which well or borehole drilling cannot continue. 

undertaking

noun
  • A promise or pledge; a guarantee. 

  • That which is undertaken; any business, work, or project which a person engages in, or attempts to perform; an enterprise. 

  • The business of an undertaker, or the management of funerals. 

  • The act of one who undertakes (in either sense). 

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