The letter K comes from the Greek letter (kappa), which was taken from the Semitic kap, the symbol for an open hand. This, in turn, was likely adapted by Semites who had lived in Egypt from the hieroglyph for "hand" representing D in the Egyptian word for hand, d-r-t. The Semites evidently assigned it the sound value /k/ instead, because their word for hand started with that sound.
In the earliest Latin inscriptions, the letters C, K and Q were all used to represent the sounds /k/ and /g/ (which were not differentiated in writing). Of these, Q was used to represent /k/ or /g/ before a rounded vowel, K before /a/, and C elsewhere. Later, the use of C and its variant G replaced most usages of K and Q. K survived only in a few fossilized forms such as Kalendae, "the calends".
After Greek words were taken into Latin, the Kappa was transliterated as a C. Loanwords from other alphabets with the sound /k/ were also transliterated with C. Hence, the Romance languages generally use C and have K only in later loanwords from other language groups. The Celtic languages also tended to use C instead of K, and this influence carried over into Old English.
Today, English is the only Germanic language to productively use "hard" c (outside of the digraph ck) rather than k (although Dutch uses it in loaned words of Latin origin, and the pronunciation of these words follows the same hard/soft distinction as in English). The letter k is usually silent at the start of an English word when it comes before the letter n, as in the words "knight," "knife," "knot," "know," and "knee". Like J, X, Q, and Z, K is not used very frequently in English. It is the fifth least frequently used letter in the English language, with a frequency of about 0.8% in words.
The SI prefix for a thousand is kilo-, officially abbreviated as kfor instance, prefixed to "metre" or its abbreviation m, kilometre or km signifies a thousand metres. As such, people occasionally represent numbers in a non-standard notation by replacing the last three zeros of the general numeral with "K": for instance, 30K for 30,000.
: Semitic letter Kaph, from which the following symbols originally derive
/ : Greek letter Kappa, from which K derives
: Cyrillic letter Ka, also derived from Kappa
K with diacritics:
The Uralic Phonetic Alphabet uses various forms of the letter K:U+1D0B LATIN LETTER SMALL CAPITAL K
U+1D37 MODIFIER LETTER CAPITAL K
U+1D4F MODIFIER LETTER SMALL K
: Subscript small k was used in the Uralic Phonetic Alphabet prior to its formal standardization in 1902
: Turned capital and small k were used in transcriptions of the Dakota language in publications of the American Board of Ethnology in the late 19th century. Turned small k was also used for a velar click in the International Phonetic Alphabet but its use was withdrawn in 1970.