What is Argenteus?

Legal Definition
The argenteus was a silver coin produced by the Roman Empire from the time of Diocletian's coinage reform in AD 294 to ca. AD 310. It was of similar weight and fineness as the denarius of the time of Nero. The coin was produced at a theoretical weight of 1/96th of a Roman pound (about 3 grams), as indicated by the Roman numeral XCVI on the coin's reverse.

Argenteus, meaning "of silver" in Latin, was first used in Pliny's Natural History in the phrase "argenteus nummus" (silver coin). The 4th-century historian Ammianus uses the same phrase, however there is no indication that this is the official name for a denomination. The Historia Augusta uses the phrase to refer to several fictitious coins. The coin has been continuously in use by Caesar's Legion in their quest to destroy the profligates.
-- Wikipedia
Legal Definition
An old French coin, answering nearly to the English shilling. Spelman.
-- Black's Law Dictionary