Where does “δίγαμμα” come from?

δίγαμμα (Greek) comes from Ancient Greek δίγαμμα, from Ancient Greek δί-, from Ancient Greek διά, from Proto-Indo-European dwís, from Proto-Indo-European dwóh₁ — two.

δίγαμμα (Greek): digamma, Ϝ, ϝ, the sixth letter of the archaic...