Matthew 20:2

For a penny [ε κ δ η ν α ρ ι ο υ]. A denarius, the chief silver coin of the Romans at this time, and of the value of about seventeen cents. We must remember to reckon according to the rate of wages in that day. A denarius was regarded as good pay for a day's work. It was the pay of a Roman soldier in Christ's time. In almost every case where the word occurs in the New Testament it is connected with the idea of a liberal or large amount. Compare Matthew 18:28; Mark 6:37; Luke 7:41; John 12:5.

For a penny is, literally, out of or on the strength of a penny; the payment being that on the strength of which the agreement was made. The agreement arose out of the demand on the one hand and the promise on the other.