E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Filthy pelf. Money. The word was anciently used for refuse or rubbish. Who steals my purse steals trash. Filthy means ungodly; the Scripture expression is unrighteous mammon. It is certainly not connected with pilfer, as it is usually given; but it may possibly be with the Anglo-Saxon pila, a pile or heap.