Thayer's Greek Lexicon

 denarius = "containing ten"
1. A Roman silver coin in NT time. It took its name from it being
equal to ten "asses", a number after 217 B.C. increased to
sixteen (about 3.898 grams or .1375 oz.). It was the principal
silver coin of the Roman empire. From the parable of the
labourers in the vineyard, it would seem that a denarius was then
the ordinary pay for a day's wages. (Mt. 20:2-13.