Digamma

The digamma (Greek δίγαμμα, majuscule Ϝ/Ͷ, minuscule ϝ/ͷ) was originally the sixth letter of the Greek alphabet, but fell out of use around 500 BC. It had the phonetic value [w] and descended from the Phoenician letter "waw". The descriptive name Digamma ("double gamma"), already in ancient Greek, is based on its F-shaped form (two right-turned "gallows" laid on top of each other, with a common upward stroke, make an F) and indicates that the sound originally represented had already fallen into disuse in some dialects of classical Greek antiquity, especially Attic-Ionian, while Doric dialects preserved this sound longer. According to the Milesian system, it has the numerical value 6.

Source

The digamma, like the ypsilon, derives from the Phoenician letter waw ( ) for [w]. When the Phoenician alphabet was adopted, the consonantal digamma (Ϝ) for [w] and the vocalic ypsilon (Υ), which originally had the phonetic value [u], were developed from the Phoenician waw. The digamma stood in the same place in the alphabetical order as the Phoenician waw, namely in the sixth place between epsilon and zeta, the ypsilon being appended to the end of the alphabet. The original name of the digamma is unknown, but by analogy with the development of the name of the letter tau (Phoenician taw → Greek tau) it may be assumed that it was ϝαῦ waú (because of Phoenician waw).

Use as a letter

Greek had originally adopted the [w] sound from Proto-Indo-European. The digamma is equivalent to a w in related German words (which, however, has the phonetic value v), and to a v in Latin words (phonetic value w; cf. gr. οἶνος oînos, formerly ϝοῖνος woînos, with dt. wine and lat. vinum or gr. εἰδέναι eidénai, formerly ϝειδέναι weidénai, with dt. know and lat. videre).

In some dialects, including Attic, the classical form of ancient Greek, this sound fell out early. Therefore, there was also no use for the letter digamma. When the Milesian alphabet was introduced in Athens in 403 BC, the digamma, which had become superfluous, was abolished.

In those dialects which still possessed the [w] sound, the use of the digamma is attested by inscriptions. There is also evidence of the presence of the digamma in poetry, especially in Homer, Sappho, and Alkman.

The w sound in early Greek was rediscovered by Richard Bentley (1662-1742) when he attempted to reconstruct the meter in Homer's epics. Words that originally began with digamma occur in Homer more than 3000 times in places where the meter requires a consonantally sounding word. In Homer's time, the digamma was probably no longer spoken, but it still had some effect in orally transmitted verses.

The archaic inscription [...]Ι ϜΑΝΑΚΤΙ ([poteidan]i wanakti) on this ceramic fragment corresponds to the word ἄναξ (ánax, "prince") in classical Greek.