guarantee
US /ˌɡer.ənˈtiː/
UK /ˌɡer.ənˈtiː/

1.
a formal promise or assurance that certain conditions shall be fulfilled, especially that a product will be repaired or replaced if not of a specified quality and durability
:
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The television comes with a two-year guarantee.
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We offer a money-back guarantee if you're not satisfied.
1.
2.
provide security for (a debt or obligation)
:
•
His assets were used to guarantee the loan.
•
The bank will guarantee your mortgage.