Lords of Finance by Liaquat Ahamed (pg. 76)

Once they had exhausted every potential source of loans, they relied on a technique almost as old as war itself: inflation. Unlike medieval kings, however, who accomplished this either by shaving pieces of gold and silver off the outer edge of their coins–a practice known as clipping–or of issuing coinage made of cheaper alloys–currency debasement–governments in the Great War turned to their central banks, often relying on complex accounting ruses to disguise the process. Central banks in turn, abandoning their longstanding principle of only issuing currency backed by gold, simply printed the money.