assurance / insurance
A promise or confidence versus a paid policy against loss.
Assurance is a pledge, or confidence: she gave her assurance, he spoke with assurance. Insurance is the contract that pays if a loss occurs. Do not use life assurance unless you are quoting a British policy name.
Examples
UseHe wanted assurance that the date would hold.
UseThe building has fire insurance.
AvoidThe building has fire assurance.