E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
He does not know a libel from a lupine. In Latin: Ignorat quid distent æra lupinis, He does not know good money from a counter, or a hawk from a handsaw. The Romans called counters lupines or beans. A libel was a small silver coin the tenth part of a denarius = the as.