K, 11th letter of the English alphabet, is derived from the Semitic kaph, representing the palm of the hand, and from the ancient Greek kappa. After C was given the K sound, the Romans stopped using K except as an abbreviation. K is sometimes used as an abbreviation for knight, as in K.C. (Knights of Columbus); for kilo, a prefix meaning 1,000; and in chess, for king. In chemistry K is the symbol for potassium.