If you assure someone that something is true or will happen, you tell them that it is definitely true or will happen, often in order to make them less worried. We often use such phrases as I can assure you or let me assure you in order to emphasise the truth of what we are saying:
- She hastened to assure me that the report contained no critical comment on my department's performance.
- Let me assure you / I can assure you that the children will be totally safe on this adventure holiday. No risks of any kind will be taken.
Ensure is subtly different from assure and people often confuse the two. If you ensure that something happens, you make certain that it happens. A less formal equivalent of this verb in spoken English would be make sure:
- Ensure / Make sure that your working hours as well as your rate of pay are written into your contract.
- I tried to ensure that everybody wore their life jackets the whole time that we were on the sailing boats, but not everybody carried out my instruction.
In American English, ensure is sometimes spelt insure:
- I shall try to insure that you have a nice time while you are here.
Insure has another meaning, as you suggest, Betty. If you insure yourself or your property, you pay money to an insurance company so that if you become ill or if your property is stolen or damaged, the company will pay you a sum of money:
- We can insure your car against fire, theft and third party damage for as little as £30 per month.
- Make sure you remember to insure the digital camera and the mobile phones. They're not included under the house contents insurance.
First and foremost, assurance has the same meaning as assure. If you give someone an assurance that something is true or will happen, you say that it is definitely true or will definitely happen in order to make them feel less worried:
- He sought an assurance from me that I'd always be available on Saturdays to undertake the work.
- I was unable to give her any assurance that Beth would arrive in time for the family re-union.
Secondly, in British English we sometimes talk about life assurance as an alternative to life insurance to describe the form of insurance in which a person makes regular payments to an insurance company in return for a sum of money which is paid to them after a period of time or to their family if they die. Both terms are freely used in British English:
- As we came down that hill, I thought we were going to die and I started thinking about my life insurance / life assurance policies.
Insurance is the term used to describe all other types of insurance:
- That car is not insured. The insurance expired at the end of July and you haven't renewed it.
Note that we cannot say ensurance. There is no noun which is derived from ensure.