Of all the bloody nonsense (reduced to using a Brit word)!
All the nonsense (I repeat myself) from people who know little of language and its development and evolution and try to straightjacket oral or written language.
And (not supposed to start a sentence with 'and') how words once in common usage become obsolete, then perhaps regain favor.

Even the OED tends to niggle in some definitions.
Why did ensurancer lose favor? A word that newscasters and politicians should resurrect.

But to cut to the chase-
Extracting from OED:
ensure Sure, confident. (Niggle): AF ensur "but perh. to be taken as phrase en sur in a state of security"
ensure See also insure. the AF vb may be regarded as an alteration of OF asseurer to Assure. ..."The word frequently occurs in individual MSS. of Chaucer, but the better attested reading....is app. assure. The form Insure is properly a mere variant of ensure.... and still occasionally occurs in all the surviving senses...."
1. ...to convince
2. to give security to
3. to tell (a person) confidentially that...
4. to guarantee (a thing) to a person...
5. to engage (a person) by pledge or contract...
   b. to betroth, espouse
6. to secure, make safe...
7. to insure (a person's life, property, etc.) obs.
8. To make certain the occurrence of an event, or the attainment of (a result)
9. to make a thing sure to or for a person; to secure.

Enough, only one word- lest we become enswamped in our in(en)quiry.