What is the meaning of guarantee?

noun

• A written assurance that some product or service will be provided or will meet certain specifications.
  • synonyms: warrant, warrantee, warranty
• An unconditional commitment that something will happen or that something is true.
  • usage: "there is no guarantee that they are not lying"
• A collateral agreement to answer for the debt of another in case that person defaults.
  • synonyms: guaranty

verb

• Give surety or assume responsibility.
  • usage: "I vouch for the quality of my products"
  • synonyms: vouch
• Make certain of.
  • usage: "This nest egg will ensure a nice retirement for us"; "Preparation will guarantee success"
  • synonyms: ensure, insure, assure, secure
• Promise to do or accomplish.
  • usage: "guarantee to free the prisoners"
  • synonyms: undertake
• Stand behind and guarantee the quality, accuracy, or condition of.
  • usage: "The dealer warrants all the cars he sells"; "I warrant this information"
  • synonyms: warrant