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:
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 )
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...