Definition of "Guarantee" :

noun: a written assurance that some product or service will be provided or will meet certain specifications

noun: an unconditional commitment that something will happen or that something is true

"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

verb: promise to do or accomplish

"Guarantee to free the prisoners."

verb: give surety or assume responsibility

verb: make certain of

"Preparation will guarantee success!."

verb: stand behind and guarantee the quality, accuracy, or condition of