pledge vs undertaking

pledge

noun
  • A solemn promise to do something. 

  • The personal property so pledged, to be kept until the debt is paid. 

  • A bailment of personal property to secure payment of a debt without transfer of title. 

  • A person who has taken a pledge of allegiance to a college fraternity, but is not yet formally approved. 

  • A drinking toast. 

  • An asset or person temporarily handed over to guarantee the fulfilment of something promised, under threat of permanent loss of the thing handed over; surety, security, hostage. 

  • A promise to abstain from drinking alcohol. 

verb
  • To deposit something as a security; to pawn. 

  • To make a solemn promise (to do something). 

  • To give assurance of friendship by the act of drinking; to drink to one's health. 

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 pledge and undertaking occurred in a corpus of books? (source: Google Ngram Viewer )