The narrow definition of insure as 'protect by insurance' seems fairly recent. OED2 has citations from 1724, 1825 and 1864 of insure as 'To make safe, to secure, to guarantee (against, from): = ASSURE v. 1c, ENSURE v. 6', see insure v. 6. Merriam-Webster's dictionary of English Usage (1994) has several citations of insure as ensure, from 1969, 1982, and 1986:
- '... would insure against any akward second marriage' -- Mollie Hardwick, Emma, Lady Hamilton, 1969
- '... his sudden fame probably insured a backlash' -- Calvin Tomkins, New Yorker, 6 Dec. 1982
- '... held that school officials had the right to insure that a high-school assembly proceed in an orderly manner' -- William Safire, N.Y. Times, 24 Aug. 1986
The Columbia Guide to Standard American English, Merriam-Webster's Unabridged (3rd ed.), the American Heritage Book of English Usage, the American Heritage Dictionary (4th ed.), Random House Unabridged Dictionary (2nd. ed.), the Oxford American Dictionary of Current English, the Oxford Dictionary of English (2nd. ed), and the Century Dictionary (1889) all have the definition of insure as ensure.
Garner's The Oxford Dictionary of American Usage and Style and Pocket Fowler's Modern English Usage (by Burchfield/Allen) both restrict insure to the financial sense. Insure as ensure is not accepted by everyone, but insure as ensure is certainly no recent development or attempt to generate more sales by adding fake 'new words'.
You may not want to use insure this way (like Garner and Allen), but that doesn't make anyone who disagrees with you wrong or uneducated.
