What is Denarius Dei?

Legal Definition
A term used in some countries to signify a certain sum of money which is given by one of the contracting parties to the other, as a sign of the completion of the contract.

2. It does not however bind the parties he who received it may return it in a limited time, or the other may abandon it, and avoid the engagement.

3. It differs from arrhae in this, that the latter is a part of the consideration, while the denarius dei is no part of it. 1 Duverg. n. 132 3 Duverg. n. 49; Repert. de Jur. verbo Denier a Dieu.
-- Bouviers Law Dictionary
Legal Definition
(Lat "God's penny.") Earnest money; money given as a token of the completion of a bargain. It differs from arrlug in this: that arrhae is a part of the consideration, while the denarius Dei is no part of it. The latter was given away in charity ; whence the name.
-- Black's Law Dictionary
Legal Definition
Earnest-money.
-- Ballentine's Law Dictionary