guarantee >> ɡar(ə)nˈtiː
Definition: [noun] a formal assurance (typically in writing) that certain conditions will be fulfilled, especially that a product will be repaired or replaced if not of a specified quality.
Example: we offer a 10-year guarantee against rusting
Definition: [noun] an undertaking to answer for the payment or performance of another person's debt or obligation in the event of a default by the person primarily responsible for it.
Definition: [verb] provide a formal assurance, especially that certain conditions will be fulfilled relating to a product, service, or transaction.
Example: the company guarantees to refund your money
Definition: [verb] promise with certainty.
Example: no one can guarantee a profit on stocks and shares