There is a very good book about the hot waters of Aqua Sulis, called "The Waters of the Gap" by R.J.Stewart, and here again we come to magical hot water coming out of the rock, and strangely the imagery of Dames word c**t is not too far off from gap it would have been part of prehistory, as it was of Roman and Saxon history. Stewart takes the etymology of Sulis the goddess, to the Irish Sul/Suil meaning eye, as did an earlier contributor to TMA when he listed all the words similar to Sul, though in this instance he related back to the sun as well. It is of course interesting to note that Sul is not very far from Sil, but whether one wishes to take an imaginative leap and say that there was an overarching prehistoric goddess called Sul/Sil that stretched her territory to Silbury Hill needs to be left on hold for the time being, but again if her water shrine at the roman town of Aqua Sulis holds an original name then it does to a degree tie up with Dames idea of a fertility goddess and water, the remnants of this paganism still holding out along the river of the Kennet, the Kennet itself a 'holy' river, and of course magical in its seasonal coming and going.
note; Gap Old norse for chasm, and in the Anglo Saxon Chronicle, geat is translated as gap by some, though Sweet records geat as a gate which is of course similar.
Further to Stewart's interpretation of the meaning of Sulis, he gives the following meanings;
In Irish; Suil - An eye; Also used as meaning eye or hole (of a strap)
In Gaelic; Suil - An eye; the centre of a whirlpool. An opening or orifice.
Suileath - Sharp sighted and knowing
In Manx - Shilley or sooil; an eye
He goes on to say, and here his argument is interesting for it might go back to Swallowhead or Sil, that the English verb to swallow, is derived from the same source; it is related to an Icelandic word meaning 'whirlpool'.
To understand how a word can take on several meanings, you must go back to the celtic world and its conceptual understanding of how everything is bound up in each other. In death you travel to another world, you take food and drink and your belongings; the celtic vision is a contrasting one dark/light, fire/water.
There is an interesting celtic story, of how a man came to a river and across the river there were white sheep, and a tree, one half of the tree was green, but the other half was on fire, when he had crossed the river the sheep turned black, this allusion to the changing patterns of the world, must also be seen as the framework of nature and god worship. It was fluid, Sulis the goddess represented water, but she also represented the all-seeing eye, if you look into water, your reflection is cast back at you; its depths will take you down to the otherworld.
The fact that Sil also is seen as an 'eye' is taken from this interpretation, but she is also surrounded by water, in the form of springs, and later roman wells; her moat or ditch just reinforces this power she had on the land.
Note 2; Whilst reading Seamus Heaney's Beowulf I came across the following, it is an example of how our English/Celtic language overlaps itself, it illustrates perfectly the duality of the meanings of words, how they proscribe the word themselves, the word is whiskey and its relation to water...
"whiskey" is the same word as the Irish and Scots Gaelic word uisce meaning water, and that the river Usk in Wales (which flows into the Severn Channel)is therefore to some extent the River Uisce/water (or whiskey).