According to the OED the Isle of Wight is from L. Vectis (c.150), originally Celtic, possibly meaning "place of the division."
This accords with Dan's view:
Dan wrote:
A Dan Cruikshank(?) programme caught my eye a few years ago: alum shale mining and alum production up near Whitby. Very interesting.
They pointed to a ridge of rock offshore and said that's where the coast used to be before they dug it away. The Needles look much the same, only bigger. And, bugger me, the Needles are on the edge of Alum Bay... which the telly prog said was named because they didn't find any alum there when they were looking for domestic sources in the 15th century (or so)!!!
I'm seriously entertaining the notion that the Solent was dug out on the left hand side, making Wight an Isle.