The humble farthing was for centuries the smallest coin minted for legal tender in the UK. Worth ¼ of a pre-decimal penny, there were a staggering 960 farthings to one pound sterling. The word 'farthing' derives from the Anglo-Saxon word feorthing, meaning "fourth".
Farthings were around in some form for centuries, although the coin was not standardised until
1613, when King James issued a proclamation prohibiting the production of private coinage and giving John Harrington, the then Lord of Exton a licence to produce copper farthings. The original coins should have weighed just six grains (aproximately one-third of a gram) but actually weighed only five. After public outcry over profiteering, the weight was increased to nine grains.
Initially, the cost of minting any coin, let alone one of small value, was such that the coins were hammered rather than milled. Milling produced a more standard size and weight, and the coins were less prone to "clipping", the practice of shaving minute amounts of metal off. Milling began during the reign of Charles II in the early 1660s
Once the coin was standardised, it gained in favour, and remained legal tender until 31st January 1961. I barely remember this coin, about the size of the modern decimal penny, the Queen's head on the obverse, and a wren on the reverse, but miss it, and its bigger brother, the ha'penny still.