K

Symbol for kelvin, a scale of temperature.

k

Symbol for kilo-, as in kg (kilogram) and km (kilometre).

K

Abbreviation for thousand, as in a salary of $50K.

K

11th letter of the English alphabet, derived from the Greek kappa (Κ, κ) and representing the unvoiced velar plosive. In English, it is silent before n at the beginning of a word (for example, in ‘knee’), a change that probably came about in the 17th century.

The Etruscans, who adopted the Greek alphabet, used the Greek gamma (Γ, γ) for both /g/ and /k/. They had two further signs, k and q, for the sound /k/. The Latin alphabet adopted these three signs. The k was later dropped, and c used for both /k/ and /g/. The letter q, when followed by u, was also used for the sound /k/. K does not therefore occur in Old English, but appeared in early Middle English as a variant of c. Middle English c had the hard sound /k/ before e and i, but with the Normans, words of French origin were absorbed in which c had the sound /s/ before e and i. For clarity the words of native origin began to be written with a k. There are many words of Scandinavian origin with initial k in English, such as ‘keg’, ‘kilt’, and ‘kirk’, and many other words have been introduced, such as ‘koran’ and ‘kangaroo’.