Digamma

Digamma (or wau, uppercase Ϝ, lowercase ϝ; as a numeral: stigma, ϛ) is an archaic letter of the Greek alphabet, which originally stood for the sound /w/ and later remained in use only as a symbol for the number "6". Whereas it was originally called wau, its most common appellation in classical Greek is digamma, while, as a numeral, it was called episēmon during the Byzantine era. Today, the numeral is often called stigma, after the value of a Byzantine Greek ligature σ-τ (ϛ), which shares the same shape and was used as a textual ligature in Greek print until the 19th century.

Digamma/wau was part of the original archaic Greek alphabet as initially adopted from Phoenician. Like its model, Phoenician waw, it represented the voiced labial-velar approximant /w/ and stood in the 6th position in the alphabet, between epsilon and zeta. It is the consonantal doublet of the vowel letter upsilon (/u/), which was also derived from waw but was placed at the end of the Greek alphabet. Digamma/wau is in turn the ancestor of the Latin letter F. As an alphabetic letter it is attested in archaic and dialectal ancient Greek inscriptions until the classical period.

The shape of the letter went through a development from through, to or, which at that point was conflated with the σ-τ ligature . In modern print, a distinction is made between the letter in its original alphabetic role as a consonant sign, which is rendered as "Ϝ" or its modern lowercase variant "ϝ", and the numeric symbol, which is represented by "ϛ" (or, in modern practice in Greece, replaced with "στ").