E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Money paid down on the nail; ready money. The first of the psalms appointed to be read on the twenty-fifth morning of the month is entitled Legem pone, and March 25th is the great pay-day; in this way the phrase Legem pone became associated with cash down.
In this there is nothing to be abated; all their speech is legem pone.Minshall: Essayes Prison, p. 26.
They were all in our service for the legem pone.