Stigma (letter)

Stigma (ϛ) is a ligature of the Greek letters sigma (Σ) and tau (Τ), which was used in writing Greek between the Middle Ages and the 19th century. It is also used as a numeral symbol for the number 6. In this unrelated function, it is a continuation of the old letter digamma (originally Ϝ, cursive form ), which had served as a numeral since antiquity and was conflated with the σ-τ ligature in the minuscule handwriting of the Middle Ages.

The στ ligature (, ) was one of many ligature forms that came into widespread use as part of the minuscule writing style of Greek from the 9th and 10th centuries onwards. It is based on the lunate form (Ϲ) of the letter sigma.

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