The Roman’s won the day
About par for the course … what have the Romans ever done for us, eh? 😀
More seriously, going back to Figgy Dowdy and Carn Marth, my own hunch, gut feeling and instinct even though I cannot prove anything is that it’s a mixture of our first two hypotheses. For me the water connection, the corrupted name from Cornish and the possible later association with being a witch are highly suggestive and strong indications that something very old has been half-remembered here. Similar things happen in Welsh folklore with witches and giants. In this case, if it is indeed what I think, there has most definitely been some Christianisation, but this is “folk Christianity” a veneer of Christianity on something ancient.
What do you think?