Numus, or Nummus, the name by which the Romans denoted a coined piece of metal. The word seems to be derived from the Greek NOMOS (nomos), although among the Greeks the word NOMISMA (nomisma) was more in use, whence the Latins wrote Numisma, which signifies what (from the French monnoie) we call money: namely pieces of metal bearing the impress of different signs, indicative of their weight and value, which, for the public accommodation and benefit, are ordained by law to circulate in exchange for the necessaries and luxuries of life, and to facilitate the otherwise too difficult means of conducting commercial transactions, but the liberty of fabricating which was denied to private individuals.
Numus = Goverment sanctioned money, mostly used when talking about coins.