*Cornelius Tacitus: Roman historian & politician (55 AD – 117 AD)
“K, eleventh letter of the alphabet. It corresponds to the Semitic kaph and the Greek kappa (Κ). It has changed its shape less perhaps than any other letter in the history of the alphabet.
The letter k may have started as a picture sign of the palm of the hand, as in Egyptian hieroglyphic writing and in a very early Semitic writing used about 1500 BCE on the Sinai Peninsula. About 1000 BCE in Byblos and other Phoenician and Canaanite centres, the sign was given a linear form, the source of all later forms. In the Semitic languages the sign was called kaph, meaning “palm.” The Greeks changed the Semitic name to kappa. They also turned the letter around to suit the left-to-right direction of their writing. The Romans took the sign over into Latin, but they used it sparingly. From Latin the capital letter K came into English unchanged.
The Semitic form may derive from an earlier sign representing a bent hand. Early Greek forms from the island of Thera have some resemblance to the Semitic. The Chalcidic, Etruscan, and Latin forms were identical, and the letter has retained its shape until modern times. The minuscule form k is but a slight adaptation of the majuscule with the point of junction of three strokes lowered and the lower transverse stroke consequently much shortened and moved to the right. A rounded form also appears in handwriting.
The sound represented by the letter throughout its known history until the present day has been the unvoiced velar stop. Its function in the Latin alphabet was usurped by the letter C, which, taken over as representing the voiced velar, came under Etruscan influence to represent the unvoiced sound as well. Later the letter G was adapted from C to represent the voiced velar and C stood for the unvoiced only. The letter K fell into disuse except in official formulas or initials such as in the word Kalendae and as a rare variant spelling in Karthago and a very few other words.
In late Latin and the early Romance period the unvoiced velar, represented by C, became palatalized before front vowels, and in the 12th century K was reintroduced as a substitute for C to represent the velar before front vowels since C did duty for both the velar and palatal in such cases and confusion was thus liable to arise. Thus the English word cyng, for example, began to be spelled kyng, later king.
In modern English orthography k is combined with c to represent the unvoiced velar when the sound is final—e.g., thick, stock, buck. This is mainly limited to monosyllables, but attack, haddock, hillock, mattock, and several other words of similar type form a small class of exceptions.
In chemistry K is the symbol for potassium (kalium).”