Why is the ninth month called September?
late 13c., from Old French contrefait "imitated" (Modern French contrefait), past participle of contrefaire "imitate," from contre- "against" (see contra-) + faire "to make, to do" (from Latin facere; see factitious). Medieval Latin contrafactio meant "setting in opposition or contrast." Related: Counterfeited; counterfeiting. The noun and adjective are from late 14c.
manufacture of false money for gain, a kind of forgery in that something is copied so as to defraud by passing it for the original or genuine article. Because of the value conferred on money and the high level of technical skill required to imitate it, counterfeiting is singled out from other acts of forgery and is treated as a separate crime