Best Guess

Here on the Onion AV Club is a comparison of the movie and book versions of Into the Wild. The comments section contains the proposition that "paragon and paradigm are synonyms", at which point I thought, "What? No they aren't!" But then just two comments later, someone else deals with this, so you can read it yourself. (Oh, very well: a paradigm is a model or example of something, while a paragon is a model of excellence. Related, but not the same, certainly not synonymous.)

What I found amusing was that in the intervening comment, someone playfully used the word "polygon" instead of "paragon", a very Mrs. Malaprop sort of thing to do, and I began to wonder where "paragon" came from, anyway.

Let's start with "polygon". It's self-evidently from the Greek, and although you'd think it ought to mean "many-sided", it actually means "many-angled": "poly-" means "many", and the "-gon" part comes from "gonia", "angle", which is descended from "gony", "knee", which gave English such words as (via Latin) "genuflect", "to bend at the knee", and in fact "knee" itself (both from Latin "genu", "knee", which in Old English became "cneo").

So "paragon" must mean something like...well, what could it mean?

It has nothing to do with knees, or angles, or anything else of the sort: it's just one of those accidents. "Paragon" starts with "para-", "alongside", all right, but the second half is not from "gony" but evidently from "akone", "whetstone". A paragon, therefore, it something that has been tested for sharpness alongside something else on a whetstone and found to be superior.

It's also interesting to note that, as in the Greek original, "paragon" in English has been used as a transitive verb, something I've never seen done and never would have guessed. It means "to rival" or "to compare". It sounds sort of wrong to me, I have to say.