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 tine 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; for the unit of currency, it is £.
The silver used for money was supposed to be very pure. The term for this 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.