A student of mine recently mentioned these three words, Assure, Ensure and Insure and was not sure about the differences. Essentially, all of them are about "making sure" but they are subtly different. Be assured that at the end of this post, you should know the difference!
First, let's talk about ensure.
Ensure basically means to confirm or make certain of something.
"Ensure that you have your keys before you leave the house."
"I will ensure that I have my passport and tickets before I go the airport."
Insure is a word often used in everyday life. You can buy insurance to protect your property or your health. Maybe you have had to make sure you insured your car before you drove it for the first time. It can also mean to make certain to do something, so can be interchangeable with ensure.
Phrasal Verb: Take (insurance) out- a specific Phrasal Verb meaning to buy insurance. (Separable Transitive)
"Did you remember to take out insurance for your holiday?"
Assure means to make certain of something or to promise or inform someone positively of something, to remove doubts. You might someone assurance and even reassurance. Assurance is sometimes used in the UK by the Insurance industry so you may see it used in advertising of these products.
"I assure you, we're doing everything we can to solve the problem."