Kinnerton Court Stone I 1
Image by postman
Kinnerton Court Stone I

Calling morfe

It could be something to do with hiding. <i>Wimple</i> (as in a Nun's Wimpel) comes from the Indo-European root <i>wimb</i> which means veil or even banner. Perhaps it just looks like a wimple?

There are cognates that mean <i>crown</i> too, so could it be a 'royal' hill?

most of the definitions in the oed are about awls and winnowing but also there's:

'Apparently a northern word taken up by Spenser. Recorded in modern dialect from Yorkshire and Lancashire. The immediate source is unknown.
Active, nimble.

(Scandinavian words of appropriate form (eg Norwegian 'vimmel'=giddy, confused) have not the required sense.)'

Couldn't find a Yorkshire/Lancashire dialect book..
And the wimble stone I posted is in Somerset, besides, so maybe it's not as local as that.