Webster’s Revised Unabridged Dictionary · 1913
Digamma
Di·gam′ma (dī·găm′mȧ), n. [Gr. δίγαμμα; δι- = δίς twice + γάμμα the letter Γ. So called because it resembled two gammas placed one above the other.] (Gr. Gram.) A letter of the Greek alphabet, which early fell into disuse.
☞ This form identifies it with the Latin F, though in sound it is said to have been nearer V. It was pronounced, probably, much like the English W.