The word "cilt" is simply the Welsh spelling for kilt. Keep in mind that the Welsh don't have a tradition of kilt wearing as the Scots do. All these Welsh tartans are inventions of the last few years, and have been created by and large by a single company, the Welsh Tartan Centre.

They are marketing traditional Scottish attire to a Welsh market, essentially. But they give things a Welsh character, and one of the ways they do that is by referring to things by the Welsh names. For instance, instead of a "sporran" (which is Gaelic for purse or pouch), they call it an "ysgrepan" (Welsh for purse or pouch).

Oddly enough, I just went to the Welsh Tartan Centre web site (to make sure I was spelling "ysgrepan" correctly!) and noticed that on their web site they use the "kilt" spelling themselves. Hmmmm......

In any case, any kilt made from cloth with a non-kilting selvedge (that is, a selvedge which is not closed), will need to have a hem, regardless of whether you spell it with a "k" or a "c".