Source : Webster's Revised Unabridged Dictionary (1913)

Digamma \Di*gam"ma\, n. [Gr. ?; ? = ? twice + ? the letter ?. 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.

   Note: 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.