koppa

Koppa (, ) is an archaic letter of the Cyrillic alphabet, originally derived from the Greek letter Qoppa. Whilst it existed in the Early Cyrillic alphabet, it is no longer used in any national languages using Cyrillic. It had no sound value in Slavonic languages, and was used exclusively as a Cyrillic numeral indicating the numeric value 90, in which function it was replaced relatively early by the letter Ч, which is similar in appearance and originally had no numeric value. Isolated examples of Ч used as a numeral are found in the East and South Slavonic areas as early as the eleventh century, though koppa continued in regular use into the fourteenth. In some varieties of Western Cyrillic, however, koppa was retained, and Ч used with the value 60, replacing .
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archaic Greek letter koppa

pock