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”

Make certain of.

“Preparation will guarantee success!”

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

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”