Four words/phrases and their origins
1 - Derby. In sporting terms when two local teams play against each other it's known as a derby. Why? The original football match was a violent affair, dating from medieval times, originally played between the parishes of Ashbourne, near Derby, on Shrove Tuesday every year...and yes, they still play it with the same rules. The term 'Local Derby' was soon attached to the game and it is now used for any occasion when local teams meet in a sporting contest.
2 - Keep Your Nose Clean. You probably won't be surprised that the term originated in relation to children with runny noses. It was first recorded in the USA in 1887 and was then applied to the adult world, with the meaning of keeping yourself smart and, by extension, not getting involved in crime.
3 - Break A Leg. This one comes from the Elizabethan stage and refers to the bowing at the end of the performance where they had a line of legs. If you broke that line of legs, it was to pick up money or flowers and it meant that the audience appreciated your performance.
4 - Bloke. The word is Romany in origin and in Britain is a term used for man. Americans have used it for 200 years to mean 'stupid idiot'. Another example of two countries separated by a common language.
If there are any phrases or word usages you would like to know about, ask in the comments section. I can't guarantee to answer them all, but I will try.