[throwaway4533]

As with many other archaic words in English, I'm guessing that "Swind" and "Swynde" came from Scandinavia and Germany where they've kept their old meaning to this day:

https://en.wiktionary.org/wiki/schwinden#German

https://en.wiktionary.org/wiki/svinde#Danish

A modern example is "oxygen depletion" or "hypoxia" in English/Latin which, in Danish, is called "iltsvind" ("ilt" = oxygen, "svind" = depletion):

https://en.wikipedia.org/wiki/Hypoxia_(environmental)

https://da.wikipedia.org/wiki/Iltsvind

It is indeed related to swindle/svindle/schwindeln but I don't know when the two words "diverged": https://en.wiktionary.org/wiki/schwindeln#German

If you go back far enough, swind/svind/schwinden may also share a common ancestor with "dwindle": https://en.wiktionary.org/wiki/Reconstruction:Proto-Germanic...

[defrost]

Indeed - the Vikings (Danes) brought their language to the north of the British Isles and it spread and persisted to today.

As I can no longer edit my comment above I should mention that the original text by Bede was written by him in Latin circa AD 731, but the O.E.D. references version translated in early | middle English by other authors in the centuries that followed.

It's from one of those that the OED quotes the first written use of Swind | Swynde in <cough> "English" </cough>.

( not so much a language as a kitchen sink full of dregs )