On his blog, JP Koning discusses “dictionary money” and the ancient practice of simply redefining what “pound,” say, means.

People have historically advertised prices for wares using a word, or unit of account, the LSD unit being the most prevalent. … from the Latin librae/solidi/denarii. The monarch was responsible for declaring what these words meant. … something to the effect that a pound, or £, was worth, say … silver coin[s]. This definition was subject to change. …

Dictionary systems came to an end when the symbol for money was finally fused directly with the instrument itself. … coins never used to have denominations, or units of account, on their face. …

In the 1700s monarchs began to adopt the practice of inscribing the actual unit of account directly on the coin’s face …