Q: I am a puzzled editor. I cringe every time I see the word “insure” used in a non-financial sense in respected publications. I am under the impression (perhaps mistakenly) that “insure” should be used in regard to finances, and “ensure” in a more abstract and wider sense. I would appreciate any light that you can shed on this.
A: Three often-confused verbs—“assure,” “ensure,” and “insure”—all mean roughly “to make secure or safe or certain.” In my book Woe Is I, I used this sentence to illustrate the traditional differences among them: “I assure you,” said the grieving widow, “I ensured he was insured to the hilt.”
In standard usage, “to assure” is to set someone’s mind at rest; “to ensure” is to make certain of something; “to insure” is to issue or buy insurance against financial loss. So your understanding of the meanings of “insure” and “ensure” conforms to standard usage. The New York Times Manual of Style and Usage (1999 edition) and The Associated Press Stylebook (2000 edition) both recognize this difference between them: “insure” should be used only in the Mutual of Omaha sense, while “ensure” means to guarantee in the general (not the commercial) sense.
Some dictionaries, however, now list “ensure” as a secondary meaning of “insure.” What this means is that many educated users of the language no longer acknowledge much of a difference.
Complicating matters is the fact that in Britain, the verb “assure” sometimes means to underwrite financial loss, though most British speakers use the term the same way American do: to reassure or remove doubt.
But rest assured that your impression is correct. You’re safest sticking to it.