The tribute money; το Ì νο ìμισμα τοῦ κη ìνσου: the coin of the tribute; that is, the coin in which the tribute was paid. The reply to the question was wholly unexpected. The Pharisaic "disciples" had hoped that Christ would have taken part against the Herodians; but he gives no decision about the matter in dispute, such as they desired.
He virtually rebukes their dissimulation, and makes their own action supply the verdict which they demanded. Not seeing the drift of his request, they brought unto him a penny; a denarius (see on Matthew 18:28).
This was the amount of the capitation tax, and it was paid in Roman, not Jewish, coinage. Just at this period the Jews had no mintage of their own, and were forced to use Roman coins, which might well be called "tribute money."