The Lost Art of the Great Speech: How to Write It * How to Deliver It

Assure/ensure/insure

To assure is to promise someone, as in "John assured Mary he would be on time." To ensure means to make certain, as in "Mary gave John an alarm clock to ensure that he would be on time." To insure means to safeguard, as in "I have my home insured against fire." Although ensure and insure are pronounced alike, you should make the distinction in your written speech.