What is the meaning of ϝ?

Lower case digamma, the sixth letter of the early Greek alphabet. Its name was probably ϝαῦ (waû), later δίγαμμα (dígamma), and it represented a voiced labial-velar approximant: /w/. It is preceded by ε and followed by ζ.

The letter δίγαμμα (dígamma).

Source: wiktionary.org