To make a pledge to (someone); to promise, guarantee (someone of something); to assure.

To make sure or certain of something (usually some future event or condition).

“I use an alarm clock to ensure that I get up on time.”

To provide for compensation if some specified risk occurs. Often agreed by policy (contract) to offer financial compensation in case of an accident, theft or other undesirable event.

“I'm not insured against burglary.”

To deal in such contracts; subscribe to a policy of insurance