dĭgammon — Lewis & Short
dĭgammon, i, or dĭgamma, ătis, n., also dĭgammos, i, f. (sc. littera), = di/gammon (sc. stoixei=on) or di/gamma,
I the Aeolic double gamma or digamma (v), represented in Latin sometimes by V, sometimes by F, which, written upside down, thus, F, the Emperor Claudius wished to substitute for both F and V, Quint. 1, 7, 27; cf. Tac. A. 11, 14; Suet. Claud. 41 (v. the letters F and V).
(a) Digammon, Quint. 1, 4, 7 Zumpt and Meyer N. cr.; Prob. Verg. G. 1, 70; Don. p. 1736 P. Lind. N. cr.; Cassiod. p. 2292 P.—
(b) Digammos littera, Ter. Maur. p. 2387 P.;
and simply digammos,Serv. Aen. 1, 292; 642; 6, 359; Pompei. ad Don. p. 21 Lind. N. cr.—
(g) Digamma, Prisc. p. 542 P.; 545 fin. ib.; 709 ib. al.—
II Used jestingly to denote an incomebook (from the title Fundorum reditus, the first letter of which is a digamma), Cic. Att. 9, 9, 4.