One of our readers recently asked about the differences between assure, ensure, and insure. All three of these words ultimately derive from the Latin word sēcūrus meaning “safe.” As with many words that share ancestors, these terms’ meanings overlap thematically, but they’re not necessarily interchangeable. Here’s a look at the key differences.
Assure was the first of the three to enter English with a reflexive sense of “to have confidence, trust, rely.” Today, the term is most commonly used to mean “to state with confidence to” or “to cause to know surely,” conveying the action of putting someone’s mind at ease, as in She assured us that everything would turn out all right.
Ensure entered English shortly after assure with the meaning “to declare earnestly to; state with confidence to.” Today it is widely used to convey the action of securing or guaranteeing an outcome or development, as in This letter will ensure you a hearing.
Insure entered English as a variant of ensure. However, in the mid-1600s, insure picked up a financial sense of “to pay a sum to secure indemnity to or on, in case of loss, damage, or death.” This financial sense is what distinguishes it today. Nowadays, we primarily use insure to talk about providing or obtaining insurance, as in After all his car accidents, the company refuses to insure him again. Insure can be used to talk about other kinds of risk, but in that usage, the term is typically followed by the word against, as in We insured against disappointment by making an early reservation.
As you can see, all of these terms address the action of making certain or guaranteeing, but each in a slightly different way. The most important distinction to remember when trying to decide which to use is that insure is the only of the three that explicitly refers to insurance policies and financial risk.