U+03DD Greek Small Letter Digamma

The Wikipedia has the following information about this codepoint:

Digamma or wau (uppercase: Ϝ, lowercase: ϝ, numeral: ϛ) is an archaic letter of the Greek alphabet. It originally stood for the sound /w/ but it has remained in use principally as a Greek numeral for 6. Whereas it was originally called waw or wau, its most common appellation in classical Greek is digamma; as a numeral, it was called episēmon during the Byzantine era and is now known as stigma after the Byzantine ligature combining σ-τ as ϛ.

Digamma or 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 near the end of the Greek alphabet. Digamma or 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". In modern Greek, this is often replaced by the digraph στ.