Why is Celtic pronounced Keltic and Seltic?

Question

As in Celtic Circle and Celtic Rangers.

Answer 1

The word is believed to have originated in an early Continental Celtic language, but it comes to us from Greek (Keltoi), where it is spelled with a kappa; thus /k/ is the original pronunciation. This was borrowed into Latin (Celtae), where it was likewise pronounced /k/. However in Mediaeval Latin, the letter <c>, originally pronounced /k/, shifted to /s/, a process known as palatalization, and many words and names borrowed from Latin into English after this sound shift are pronounced this way: centre, Cicero, et cetera. Thus /s/ is the inherited pronunciation in English.