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
“They were all in our service for the legem pone.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894