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This word can confuse us all. It has many meanings, of which two are significant to all of us in our daily lives. If someone says “Get me a pound of cherries”, the hearer may ask for clarification: “Do you mean a pound in weight, or a pound in price?” The reason for this ambiguity is quite simple – if you know it.

Originally (in Anglo-Saxon times, more than a thousand years ago), the unit of currency was called a ‘pound’, because it was represented by silver weighing a pound. (The British pound was equivalent to 454 grams.) The unit of ‘one pound’ was divided into 240 – pennyweights of weight (= 22 1/2 grains); and pennies of currency. As time – and inflation – passed, it became confusing to have two different units with diverging values called by the same name. So the two denotations were written with different abbreviations – both derived from the Latin librum, or ‘pound’. The abbreviation for the unit of weight is lb (two letters from librum); for the unit of currency, it is £ (the first letter of librum, written elaborately).

The silver used for money was supposed to be very pure. The term for this purity among jewellers and metallurgists is sterling silver. So if you happen to use pounds sterling, you are using a very ancient (and currently inaccurate) word.

Nowadays, the units of weight used for trading are those of the metric system – the gram, kilogram etc. This is now legally required. However, older people find it much easier to use the traditional British system.

See pound avoirdupois for more detail about the pound as a unit of weight; see Pounds, shillings and pence for more about the pre-1971 British currency.