Note: Do not rely on this information. It is very old.
KK, k, the eleventh letter in the English alphabet, derived from the Egyptian hieroglyphics of a bowl, called Kaph by the Phoenicians, and then by the Greeks Kappa: it was only used in Latin in Kalendae and proper names, and therefore does not appear in Romance alphabets. This letter represents the sound of the back palatal voiceless stop or explosive formerly called the hard guttural mute. It is used for this sound in Modern English in words of early English or Romance origin before e, i, and n. It is never doubled, but is used with c for double c and double k. It is also used in the writing of the middle ages as a numeral for 250.