guarantee

(noun) a written assurance that some product or service will be provided or will meet certain specifications. Synonyms: warrant, warrantee, warranty.

(noun) an unconditional commitment that something will happen or that something is true. Example: "There is no guarantee that they are not lying."

(noun) a collateral agreement to answer for the debt of another in case that person defaults. Synonyms: guaranty.

(verb) give surety or assume responsibility. Synonyms: vouch. Example: "I vouch for the quality of my products."

(verb) make certain of. Synonyms: ensure, insure, assure, secure. Examples: "This nest egg will ensure a nice retirement for us." "Preparation will guarantee success!."

(verb) promise to do or accomplish. Synonyms: undertake. Example: "Guarantee to free the prisoners."

(verb) stand behind and guarantee the quality, accuracy, or condition of. Synonyms: warrant. Examples: "The dealer warrants all the cars he sells." "I warrant this information."