ensure vs forfeit

ensure

verb
  • To make sure or certain of something (usually some future event or condition). 

  • To make a pledge to (someone); to promise, guarantee (someone of something); to assure. 

forfeit

verb
  • To suffer the loss of something by wrongdoing or non-compliance 

  • To fail to keep an obligation. 

  • To lose a contest, game, match, or other form of competition by voluntary withdrawal, by failing to attend or participate, or by violation of the rules 

  • To be guilty of a misdeed; to be criminal; to transgress. 

adj
  • Lost or alienated for an offense or crime; liable to penal seizure. 

noun
  • Something deposited and redeemable by a sportive fine as part of a game. 

  • A penalty for or consequence of a misdemeanor. 

  • A thing forfeited; that which is taken from somebody in requital of a misdeed committed; that which is lost, or the right to which is alienated, by a crime, breach of contract, etc. 

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