Guarantee
From ACT Wiki
1.
To assume the liability for debts of another in the event of the other's default.
2.
The undertaking so given.
In English law, a stronger form of security would be a bond, a bond being a direct primary obligation from the issuer of the bond, such as a bank or insurance company.
See also
Other links
Bank guarantees, letters of credit and performance bonds, The Treasurer 2013