In a post about Adam Lambert’s Rolling Stone cover, The Daily Beast’s Johanna Piazza confused insure and ensure, and none of the web site’s editors caught the error:
What the story did do, though, was re-brand the 27-year-old star in a way that Idol contestants have rarely branded themselves—as an “other,” hence insuring him the kind of celebrity rarely heaped up the second-place finisher of the competition.
Insure means to guarantee against loss or harm with a contract of indemnity (an insurance policy).
Ensure means to secure, guarantee, to make sure or certain.
Close, but there’s an important difference between the two words.