The software comes with a 'money-back guarantee'. [=a promise that the money you spend on a product will be returned if the product is not good enough]
We used our house as a 'guarantee' for the loan. [=we said that the bank could take our house if we did not pay back the loan]
There is no 'guarantee' that they will approve the contract. [=there is no way to be sure that they will approve it]
(..) I have a feeling, too. Listen, I got to go, but... ...I wanted to tell you that it's been educational. LORRAINE: Marty, will we ever see you again? I guarantee it. Well, Marty, I want to thank you for all your good advice. I'll never forget it. Right, George. Well, good luck, you guys. (..)1985 Back to the Future