Assure (verb)

1. To tell someone that something will happen or is true in a confident and definite way.
2. To give someone confidence or reassurance.
3. To make certain or secure something.
4. To promise or guarantee something.

Origin:

Middle english: from old french asegurier, from medieval latin assicurare, from ad- "to" + segurare "make secure", from latin securus "safe".

Examples:

1. He assured her that everything would be alright.
2. The doctor assured me that the surgery would be successful.
3. The company assured its customers that their personal information is secure.
4. He assured the investors that their money is safe.
5. She assured me that she would be on time.