E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Bos[ei] in lingua.
He is bribed to silence; he has a coin (marked with a bulls head) on his tongue. Adalardus, in Statutis Abbati Corbeiensis (bk. i. c. 8), seems to refer to the bos as a coin. Boves et reliquam pecuniam habeat unde et ipse et omnis familia ejus vivere possit (i.e. plenty of gold and silver ). Plautus, however, distinctly says (Persa, ii. 5, 16), Boves bini hic sunt in crumna (Two bulls in a purse.) The Greeks had the phrase, o ε Servius tells us that even the Romans had a coin with a bull stamped on it. (See Pliny, 18, 3.) Presuming that there was no such coin, there cannot be a doubt that the word Bos was used as the equivalent of the price of an ox.