In Welsh cil* means corner, 'tucked away place' or something along those lines - you may remember the name of the village with the castle with the stairs and deathleap was Cilgerran, which means something like 'Slate Corner'. It was the local quarry & major slateworks 150 years back, and the castle is indeed sited on a bend in the river. Welsh place names are often simply and directly descriptive like that, describing key topographical features.

http://family-tree.hypermart.net/a_welsh_glossary.htm


fwiw, the castle:

http://www.castlewales.com/cliger.html