guarantee

give surety or assume responsibility

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

promise to do or accomplish

“guarantee to free the prisoners”

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

make certain of

“Preparation will guarantee success!”

a collateral agreement to answer for the debt of another in case that person defaults

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

“there is no guarantee that they are not lying”