from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
DENARIUS DEI. 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.