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'll have it. - I'm going to speak Italian to Mikey. - Go ahead. What I want... What's most important to me is that I have a guarantee. No more attempts on my father's life. What guarantees can I give you? I'm the hunted one! I missed my chance. You think too much of me, kid. (..)1972 The Godfather
(..) but drugs is a dirty business. It doesn't make any difference to me what a man does for a living. But your business is... a little dangerous. If you're worried about security, the Tattaglias will guarantee it. - The Tattaglias would guarantee our... - Wait a minute. I have a sentimental weakness (..)1972 The Godfather