Explaination Of Australian Pre-Decimal Definitions

The "d" is short for "denarius", which was effectively the Latin word for "penny". The denarius was a silver coin in ancient Rome; the Mediaeval English/European penny was an attempt to make a coin of equivalent value.

The predecimal system was also known as the LSD system (also written £sd). "L" stands for libra, the old Roman pound weight. "S" for solidus, a small Roman/Byzantine gold coin. "D" for denarius. These were the monies of account - what the accountants and bookkeepers recorded wealth in, even when no actual coins matching those denominations were made. The divisions of 12 denarii to the solidus, 20 solidii to the libra were early mediaeval in origin.